Apparent movement and phases of the moon. Orientation by the sun, moon and stars The crescent moon is convex to the right and close to the horizon

V. N. Bespalov,
boarding school No. 4, Voronezh

Light. Optical phenomena. 9th grade

Lesson explaining new material using cartoon frames

It’s a pity that astronomy as an academic subject is leaving schools. Integration with physics may be useful, but physicists are unlikely to spend much time studying astronomical phenomena. And schoolchildren will lose a lot. Agree, studying the solar system in the 5th grade is unlikely to remain in the memory of students, and within the framework of the theory of relativity, of course, no one will talk about summer and maternity time. And now from the big screen we hear: “METEOR strikes caused the death of dinosaurs,” “...summer time is 2 hours ahead of standard time,” etc. Many begin to believe that stars are falling, and when moving from Astrakhan to Moscow, you can see more constellations. When studying lenses in the school curriculum, there is no time to study the structure of telescopes. And students will continue to think that “telescopes bring planets closer” instead of “telescopes increase the angle of view.” In mechanics there is no place for studying the movement of meteors and meteorites. And some begin to believe that stars are falling. But let's not talk about sad things.

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The proposed lesson can be taught when studying the rectilinear propagation of light in the topic “Optical Phenomena.” For this lesson I madeDVD-disc, digitized and re-voiced recordings on video cassette of 1991 programsd. Of course, the quality leaves much to be desired. It would be nice if our Ministry of Education produced 5-10 minute films for lessons, as they did 15-20 years ago. Now there are discs “Open Physics”, “Open Astronomy”, but I would still like to have films. Maybe I violated the copyrights of our animators, but showing fragments of cartoons in physics lessons allows you to look at the video material from the other side - educational.Once upon a time, the Rossiya channel showed
26 episodes of the Canadian animated series "The Magic School Bus". From a pedagogical point of view, it would be useful in extracurricular activities, and fragments could be included in physics, biology, and astronomy lessons. But where can I get this cartoon? I have VCR recordings, I play some things in class, but now I want to have recordings of higher quality, because multimedia projectors have appeared in schools.

At the end of the lesson, you can show a two-minute film about eclipses as a consequence of the rectilinear propagation of light and solve 2-3 problems from the book WHAT??Malakhova G.I.., Strout E.K.

After this lesson, the students wanted to know more about the Moon, so I organized a question and answer evening where I showed old recordings onDVD-discs films about the Moon. Students who had experience participating in school CPD also answered questions.

Lesson Objectives: find out what light is; understand why we see light sources and bodies that are not sources; why the appearance of the Moon in the sky changes; learn to calculate the wavelength of radiation if its frequency is known, draw the location of the Earth, Sun and Moon and determine the time of day (evening, morning) at different lunar phases, teach terrain orientation based on the phases of the Moon; conduct observations of the Moon over several evenings.

Teacher. Life on Earth arose and exists thanks to the radiant energy of sunlight. The fire of a primitive man, oil, the fuel of a space rocket - all this is light energy, once stored by plants and animals. What do you think will happen if the Sun goes out? Stop the solar flow, and rain of liquid nitrogen and oxygen will fall on the Earth. The temperature will approach absolute zero, i.e. to –273 ° C. A seven-meter shell of frozen atmospheric gases will cover the earth's surface. Only sometimes in this icy desert you will find puddles of liquid helium.

According to astronomers, the Sun will remain in a stationary stage for a long time. And all this time it will bring warmth and light to the Earth. What can you learn from the sun's rays? Thanks to the light flux, we perceive and understand the world around us. Rays of light tell us about the position of close and distant objects, their shape and color. In a homogeneous medium, rays propagate rectilinearly.

What is light? Light is electromagnetic radiation perceived by the human eye. The wavelengths of this radiation are very short and lie in a narrow range - from 0.38 to 0.77 microns (380–770 nm).Light is electromagnetic in nature. ( On the screen or on the interactive whiteboard is the table “Radiation and Frequency”. )

Tasks “Types of radiation”

What type of radiation are electromagnetic waves with a frequency of 30 GHz? 600 THz? 100 kHz? 1200 THz?

Calculate the wavelengths of these radiations.

Sources of light

Teacher. Let's fill out the table ( Students name the light sources, and the corresponding table cells “open” )/

Natural sources	Artificial sources
Auroras
	Screens of switched on TVs
Glowing insects

We see radiation sources because the radiation they create hits our eyes. But we can also see bodies that are not sources of radiation. Why? It's all about the reflection of light. We see only illuminated bodies. In the dark, all cats are gray because there is no light, which means it is not reflected from the object. Democritus was the first to understand that the Moon shines from reflected sunlight. Depending on the position of the Sun, Earth and Moon, the appearance of the Moon is constantly changing.

Study of lunar phases

(A 2.5-minute video is shown . Here is the announcer's text .) It’s as if a person has been running along a lunar path all his life. The first time he set foot on it, he raised his head and asked himself: “Why is the Moon so different: today it’s round, and tomorrow it’s crescent-shaped?” After thousands of years, he realized: the Moon shines with light reflected from the Sun. And it revolves around the Earth. During this journey, the Moon is between the Earth and the Sun, so the dark side of the Moon is turned towards us, and we do not see it. It's a new moon.

After about 7 days, the first quarter begins. The right half of the Moon is visible in the southern sky during sunset. Around midnight, the Moon will set below the horizon in the western sky.

About 7 more days will pass and we will see the full Moon. It appears in the evening in the eastern sky. Now the Earth is located between the Moon and the Sun. At midnight, the full Moon will be at its maximum height in the south.

But midnight is not 0 o'clock. In Voronezh, midnight occurs at 0:23 in winter and at 1:23 in summer. In Moscow - at 0:30 and 1:30, respectively. In other administrative centers - at different times. (See “Time zones on the territory of Russia” in the newspaper “Geography-PS”,
No. 39/2001. The line for the Tomsk and Kirov regions is subject to correction: now in Tomsk the time of the VI time zone has been introduced instead of VII, and in the Kirov region - the III time zone instead of IV, so the time of noon must be reduced by 1 hour).

After midnight, the height of the Moon begins to decrease, and in the morning in the western sky the full Moon will set below the horizon.

The next phase of the Moon is the last quarter. The moon appears in the east at midnight and will be visible until the morning. When the Sun rises, the old month will seem to “dissolve” in the southern side of the sky...

This is how the man explained to himself what lunar phases are. And the Moon became a little clearer, as if closer.

Filling out the Moon Phases table

(There is an empty table on the screen; when explained, the corresponding cells “open” .)

Teacher. Draw the positions of the Moon, Sun and Earth when the Moon is in its new moon phase. ( Students make a schematic drawing. )

What if the Moon is in its first quarter phase? ( Students make a drawing .)

Seeing an incomplete disk of the Moon in the sky, not everyone can accurately determine whether the month is young or in decline. The narrow crescent of the newly born month and the crescent of the old Moon differ only in that their convexities face in opposite directions. In the Northern Hemisphere, the young month is always directed with its convex side to the right, the old one - to the left. In the middle latitudes of the Southern Hemisphere, the opposite is true.

Problems “Phases of the Moon in Animated Films”

1. Showing a fragment from the cartoon “Holidays in Prostokvashino”.

On the screen is Uncle Fyodor, a cat and a dog. “This is probably the camera gun that came to me,” says the dog. Everyone sighs. And above the house you can see a narrow crescent of the month convex to the right.

? What time of day did the photo gun “arrive”? Draw the location of the Moon, Earth and Sun.

Clue . Please note: the month is narrow (why?). We conclude: The sun is somewhere nearby (where? in which direction?), the sky is not completely dark (why?). We see only bright stars.

2. Showing a fragment from the cartoon “The Tale of the Seven Knights”.

Tsarevich Elisha turns to the month with a request to find the princess. To which the month replies: “My brother, // I have not seen the red maiden. //I stand on guard //Only in my turn. //The princess, apparently, //ran away without me.” “What a shame,” Elisha sighs. On the screen there is a narrow crescent of the month, convex to the left.

? Which month (young or old) is Prince Elisha talking to?

Clue. The month is low above the horizon. In which direction will he move?

3. Showing a fragment from the cartoon “The Bremen Town Musicians”.

On the screen Troubadour: “The ray of the golden sun of darkness was hidden by a veil. //And suddenly a wall grew between us again.//The night will pass, the stormy season will pass, the Sun will rise.”

? On which side of the horizon is the Moon visible?

Clue. On the screen we see the full Moon low above the horizon. When does the full moon rise? When does it set over the horizon?

4. Showing a fragment from the cartoon “Three from Prostokvashino”.

Uncle Fyodor and his friends are looking for treasure.

? What time of day is it at this time?

Clue. What month do you see? Which direction should he move?

5. Showing a fragment from the cartoon “Three from Prostokvashino”.

Postman Pechkin knocks on the door. And above the house you can see a narrow crescent of the month convex to the right.

? Which direction of the horizon do the windows face?

6. Showing a fragment from the cartoon “Snowman-Postman”.

The fox is carrying a letter. But the path is blocked by a wolf. The moon is shining.

? To what direction does the shadow fall on the horizon?

Clue. What phase does the Moon have? Where can you see her?

Mindfulness tasks or Find the error

1. Showing a fragment from the cartoon "Caterok".

? What's interesting about this slide? Where can you see the Sun high above your head?

Clue. On the slide we see both the Sun and the Moon. But which side does the month face towards the Sun?

2. Slide show from the cartoon "The Night Before Christmas".

“The last day before Christmas has passed. A clear winter night has arrived. The month majestically rose into the sky to shine on good people and the whole world.”

? What phase does a month have that has “risen” above the horizon? When can you see such a sunrise?

Clue. The moon rises above the horizon. And the Sun? ( Waiting for a response.) The sun should also rise... Who among you has seen the month rising above the horizon in such a phase?

3. Show slides from the cartoon “Three from Prostokvashino”.

Ball. It's your fault that Uncle Fyodor got sick.

Matroskin. Why me?

Ball. You gave him cold milk. And he also boasted: this is the cold milk my cow gives!

(There's a knock on the door.)

Ball. Who's there?

Ball. In this weather, they sit at home and watch TV.

? What time of day did the boy’s parents arrive? Does this phase of the Moon agree with Sharik’s phrase: “In this weather they sit at home, watch TV”?

Clue . On the first slide we see two cartoon characters, on the second - a view of the Moon from their window. Is it possible to say at what time of day a dog and a cat sort things out?

4. Showing a fragment from the cartoon “Twelve Months”.

The young month is melting.// The stars are going out in succession.

? Does the text correspond to the cartoon fragment or these slides?

Clue. On the left slide we see the month low above the horizon, on the second slide the dark sky becomes light. The stars are no longer visible. At what time of day can such a month be seen?

5. Slides from the cartoon "Twelve Months".

The red sun is coming out of the open gates!

? Where can you watch such a sunrise?

Clue. On each subsequent slide the Sun gets higher and higher. Pay attention to the trajectory of the Sun. Is this how the Sun rises in mid-latitudes? ( This is a difficult question for ninth graders. But if they cannot answer, the question can be given at home, and in the next lesson, 1-2 minutes can be spent answering. .)

Teacher. Today in class we solved problems, watched cartoons and determined the phases of the moon. Now, I think you can easily determine whether the month is young or old in the sky. If we “see” the letter “C” in the sky, this is an old, waning month. And if we get the letter “P” when we draw a straight line through the two “extreme” points of the month, then we have a growing, young month. The French have their own signs. If they see the Latin letter "R", What means premier – first, then this indicates the first quarter of the Moon, waxing. If you get the letter “ d» – dernier, last, the last phase of the moon, and the month is old.

In the southern latitudes of our hemisphere, you can notice that the crescent of the month leans strongly to one side, and closer to the equator it lies so that it seems like a boat rocking on the waves, or a light arch. In any case, it should be remembered that the young month is visible in the evening in the western part of the sky, the old one in the morning in the eastern part of the sky.

Nothing is as stunning as a total solar eclipse with its majestic, slowly unfolding beauty. In this lesson (and, if possible, in the next one) you should also consider the conditions for the occurrence of solar and lunar eclipses, because they are a consequence of the rectilinear propagation of light. In order not to overload students with video recordings, this part of the lesson can be taught in the traditional form, using the text of the textbook and tasks from the collection of didactic material on astronomy.

Blitz survey

What is light? What types of electromagnetic radiation are not perceived by the human eye? How do invisible electromagnetic radiation differ from visible radiation? Why is the Moon visible in the sky differently on different days of the month: sometimes as a narrow crescent, sometimes in the form of a disk?

Homework

Draw the location of the Earth, the Sun and the month with whom Prince Elisha spoke. Draw what the Moon looks like in the first quarter. At what time of day is it visible in this phase? Look at chapter two of the book “Entertaining Astronomy” Ya.I.Perelman and get answers to many questions regarding the appearance of the Moon. When and where are the young and old moons visible?

Answers

Types of radiation

1. 30 GHz = 0.030 THz, but 0.03 THz< 0,3 ТГц, значит, это радиоволна. Если скорость света равна произведению длины волны на его частоту, то длину волны найти легко, ведь скорость света известна и равна 300000км/с или 3 10 8 м/с.

Therefore = v/ n = 1 cm.

2. 600 THz belongs to the frequency range of visible radiation. = 500 nm.

3. 100 kHz is many times smaller than 0.3 THz, and these are radio waves. = 3 km.

4. It is easy to understand that 1200 THz is in the frequency range of ultraviolet radiation. = 250 nm.

Moon phases in cartoons

1. The month above the roof is convex to the right. It's a new month. The sickle is narrow, which means it is located close to the Sun. Summer holidays. The sun sets in the northwest, which means the month is visible on the western horizon.

2. A narrow sickle convex to the left is an old month. The sun will rise soon. Such a month is visible in the early morning on the eastern side of the horizon.

3. It is difficult to answer this question by watching a fragment of the cartoon. The full moon is visible in the evening in the east. At midnight it can be seen in the south, and in the morning - in the west. But if the song contains the words “The night will pass - the morning will come...” (future tense), and the Moon is not high above the horizon, then perhaps it is visible in the eastern direction. Or in the south, but definitely not in the west.

4. In one or two days the Moon will be in its first quarter phase. In this phase, the angle between the meridians where the Moon and the Sun are located is approximately 90°. This means that at present there is approximately 60–70° between the Moon and the Sun. The crescent of the old month is low above the horizon. The month is slowly rising above the horizon. The sun will rise soon. It will be light in about 3-4 hours. Three from Prostokvashino are looking for treasure, apparently sometime after midnight or early in the morning.

5. We see a narrow crescent of the month facing to the right. This is a young month, therefore, in front of us is the western side. This means that the windows “look” to the east.

6. It is extremely difficult to answer, because... in favorable weather, the full Moon is visible all night: in the evening, at midnight, and in the morning. We can say this: the shadow definitely does not fall to the south. In the mid-latitudes of the Northern Hemisphere, the Moon moves from left to right and passes over the point of the south. But if it is evening, then the shadow falls to the west. If it is midnight, then to the north, and if it is morning, then the shadow is directed to the east.

Mindfulness tasks (« Find errors»)

1. The sun is high above your head. This is possible in the tropical zone. The unlit part of the Moon faces the Sun. Could this be possible? Of course not.

2. Residents of the mid-latitudes of the Northern Hemisphere will say: “This is a young month, and it should be approaching the horizon in the western sky. But for some reason the month rises above the horizon. This can only happen in cartoons, never in life!”

Residents of the mid-latitudes of the Southern Hemisphere will argue: “This is the “old” month, and it will indeed rise above the horizon, but in the eastern side, and its path will go from right to left, and not as shown in the cartoon.”

3. Please note: it is an old month outside the window, which means the parents arrived early in the morning. At the same time, the phrase sounds: “In this weather, they sit at home, watch TV.” But they usually watch TV in the evenings. The artists should have painted not the morning month, but the evening one.

4. For residents of the Northern Hemisphere, this is a young month. In the rays of dawn, the evening (young) month cannot “melt”. Residents of the Southern Hemisphere 12–13 times a year watch how such a month “melts” in the rays of the morning dawn, and after it “the red Sun comes out of the open gates.” But they won’t call this a month for young people. It is still old for residents of Australia and South America. Maybe S.Ya. Marshak observed such a “picture” in the Southern Hemisphere, and, without understanding it, called it young?

5. Students know that in the middle latitudes of the Northern Hemisphere the Sun rises above the horizon, moving from left to right. From geography lessons, schoolchildren remember that only at the equator does the Sun rise at right angles to the horizon, therefore, the cartoon characters ended up in the tropics. But this happens only 2 times a year: on the days of the spring and autumn equinoxes. The teacher may say that before the New Year the Sun will rise perpendicular to the horizon at the parallel of 23.5° south latitude.

But such a snowy winter, as shown in the cartoon, does not happen in the tropics! The artists had to shift the Sun to the right as it rose above the horizon.

Literature

Bespalov V.N.. Time zones in Russia. – “Geography-PS”, No. /2001 or http://besp.narod.ru

Gromov S.V.. Physics-9. – M.: Education, 2003.

Levitan E.N.. Astronomy: Textbook for 11th grade. – M.: Education, 1994 (and all subsequent editions).

Malakhova G.I., Strout E.K. Didactic material on astronomy. – M.: Education, 1989 (and all subsequent editions).

Perelman Ya.I.. Entertaining astronomy. – M.: Nauka, 1966.

Skvortsova G. Competence-based approach: rules for setting educational goals. – First of September, No. 4, 5/2008.

The Moon is the closest celestial body to the Earth, its only natural satellite. Being at a distance of about 380 thousand km from the Earth, the Moon revolves around it in the same direction in which the Earth rotates around its axis. Every day it moves relative to the stars by about 13°, making a full revolution in 27.3 days. This period of time - the period of revolution of the Moon around the Earth in a reference system associated with the stars - is called a sidereal or sidereal month (from the Latin sidus - star) month.

The Moon does not have its own glow, and the Sun illuminates only half of the lunar globe. Therefore, as it moves in orbit around the Earth, the appearance of the Moon changes - a change in lunar phases. At what time of day the Moon is above the horizon, how we see the hemisphere of the Moon facing the Earth - fully illuminated or partially illuminated - all this depends on the position of the Moon in orbit.

If it is positioned so that its dark, unlit side faces the Earth (position 1), then we cannot see the Moon, but we know that it is somewhere in the sky near the Sun. This phase of the moon is called the new moon. Moving in orbit around the Earth, the Moon will reach position 2 in about three days. At this time, it can be seen in the evenings near the setting Sun in the form of a narrow crescent, convexly facing to the right. At the same time, the rest of the Moon is often visible, which glows much weaker, the so-called ashen light. It is our planet, reflecting the sun's rays, that illuminates the night side of its satellite.

Day by day, the crescent moon increases in width, and its angular distance from the Sun increases. A week after the new moon, we see half of the illuminated hemisphere of the Moon - a phase called the first quarter begins. Subsequently, the proportion of the illuminated hemisphere of the Moon visible from Earth continues to increase until the full moon occurs. In this phase, the Moon is in the sky in the direction opposite to the Sun and is visible above the horizon all night - from sunset to sunrise. After the full moon, the phase of the moon begins to decrease. Its angular distance from the Sun also decreases. First, a small damage appears on the right edge of the lunar disk, which has the shape of a sickle. Gradually this damage increases (position 6), and a week after the full moon the last quarter phase begins. In this phase, as in the first quarter, we again see half of the illuminated hemisphere of the Moon, but now the other, which was unlit in the first quarter. The moon rises late and is visible in this phase in the morning. Subsequently, its crescent, now convexly facing to the left, becomes more and more narrow (position 8), gradually approaching the Sun. In the end, he disappears into the rays of the rising Sun - the new moon comes again.

The full cycle of changing lunar phases is 29.5 days. This period of time between two successive identical phases is called a synodic month (from the Greek synodos - connection). Even in ancient times, for many peoples, the month, along with the day and year, became one of the main calendar units. It is not difficult to understand why the synodic month is longer than the sidereal month if we remember that the Earth moves around the Sun. After 27.3 days, the Moon will take its previous position in the sky relative to the stars and will be at point L1. During this time, the Earth, moving by 1° per day, will pass an arc of 27° along its orbit and end up at point T1. The Moon, in order to be at the L2 new moon again, will have to go through the same arc in its orbit (27°). This will take a little more than two days, since the Moon moves by 13° per day. Only one side of the Moon is visible from Earth, but this does not mean that it does not rotate around its axis. Let's conduct an experiment with the globe of the Moon, moving it around the globe of the Earth so that one side of the lunar globe is always facing it. This can only be achieved if we rotate it in relation to all other objects in the classroom.

A full revolution of the globe of the Moon around its axis will be completed simultaneously with the completion of one revolution around the globe of the Earth. This proves that the period of rotation of the Moon around its axis is equal to the sidereal period of its revolution around the Earth - 27.3 days. If the orbital plane along which the Moon moves around the Earth coincided with the orbital plane along which the Earth revolves around the Sun, then a solar eclipse would occur every month at the moment of the new moon, and a lunar eclipse at the moment of the full moon. This does not happen because the plane of the lunar orbit is inclined to the plane of the Earth's orbit at an angle of about 5°. That is why, on a new moon, the shadow of the Moon can pass above the Earth, and on a full moon, the Moon itself can pass below the Earth’s shadow. At this time, the position of the Moon's orbit is such that it intersects the plane of the Earth's orbit in the first and last quarter phases. In what cases can eclipses of the Sun and Moon occur? You already know that the direction of the Earth’s rotation axis in space remains unchanged when our planet moves around the Sun.

The position of the lunar orbital plane remains virtually unchanged throughout the year. Let's consider how this will affect the possibility of eclipses. In three months, the Earth will travel a quarter of its way around the Sun and take up its position. Now the plane of the lunar orbit will be located so that the line of its intersection with the plane of the earth's orbit is directed towards the Sun. Therefore, the Moon will cross the plane of the Earth's orbit (or be close to it) during the new moon and full moon. In other words, moving across the sky, the Moon comes to that point on the ecliptic where the Sun is at that moment, and blocks it from us. If the Sun is completely covered by the Moon, the eclipse is called total. If it happens that it covers only part of the Sun, then the eclipse will be partial. When the Moon crosses the ecliptic at a point diametrically opposite to the Sun, it itself is completely or partially hidden in the shadow of the Earth.

Lunar eclipses, like solar eclipses, can be total or partial. Conditions favorable for the onset of eclipses persist for about a month. During this time, at least one solar eclipse or two solar and one lunar eclipse can occur. The next location of the lunar orbit necessary for the onset of eclipses will be repeated again only after about six months (177 - 178 days), when the Earth has passed half of its path around the Sun. During the year, two or three solar eclipses and one or two lunar eclipses usually occur on Earth. The maximum number of eclipses per year is seven. Lunar eclipses, although they occur less frequently than solar eclipses, are visible more often. The Moon, which falls into the Earth's shadow during an eclipse, is visible throughout the Earth's hemisphere, where it is above the horizon at that time.

Plunging into the earth's shadow, the Moon acquires a reddish color of various shades. The color depends on the state of the earth's atmosphere, which, while refracting the rays of the Sun and scattering them, still transmits red rays inside the shadow cone. It takes the Moon several hours to cross the Earth's shadow. The total phase of the eclipse lasts about one and a half hours. A total eclipse of the Sun can be observed only where a small (no more than 270 km in diameter) spot of the lunar shadow falls on the Earth. The Moon's shadow moves at a speed of approximately 1 km/s across the earth's surface from west to east, so at each point on the Earth a total eclipse lasts only a few minutes (at the equator the maximum duration is 7 minutes 40 s). The path that the Moon's shadow travels is called the streak of a total solar eclipse.

In different years, the lunar shadow runs across different regions of the globe, so total solar eclipses are visible less frequently than lunar ones. So, for example, in the vicinity of Moscow the last time an eclipse occurred was on August 19, 1887, and the next time it will occur only on September 16, 2126. The penumbra of the Moon has a diameter significantly larger than the shadow - about 6000 km. Where the Moon's penumbra falls, a partial eclipse of the Sun occurs. They can be seen every two to three years. Every 6585.3 days (18 years 11 days 8 hours) eclipses are repeated in the same order. This is the period of time during which the plane of the lunar orbit makes a complete revolution in space. Knowledge of the patterns of movement of the Moon and the Earth allows scientists to calculate the moments of eclipses with a high degree of accuracy hundreds of years in advance and know where on the globe they will be visible. Information about eclipses for the coming year and the conditions for their visibility are contained in the Astronomical Calendar, and here for a longer period. Having the necessary data on upcoming eclipses, scientists have the opportunity to organize expeditions during a total solar eclipse. At the moment of the full phase, one can observe the outer, most rarefied layers of the Sun's atmosphere - the solar corona, which is not visible under normal conditions. In the past, many important information about the nature of the Sun was obtained during total eclipses.

In mid-latitudes, the Sun always rises in the eastern part of the sky, gradually rises above the horizon, reaches its highest position in the sky at noon, then begins to descend towards the horizon and sets in the western part of the sky. In the Northern Hemisphere, this movement occurs from left to right, and in the Southern Hemisphere, from right to left. An observer in the Northern Hemisphere of the Earth will see the Sun in the south, and an observer in the Southern Hemisphere will see the Sun in the north. The daily path of the Sun in the sky is symmetrical relative to the north-south direction.

2. Can the Sun be observed at its zenith in Belarus? Why?

The Sun is observed at the zenith in a belt limited by the following interval of geographic latitude: $-23°27" \le φ \le 23°27".$ Belarus is located further north, so the Sun cannot be observed at the zenith in our country.

3. Why does the Moon always face the Earth with the same side?

The Moon completes a full orbit around the Earth in 27.3 days. (sidereal month). And in the same time it makes one revolution around its axis, so the same hemisphere of the Moon always faces the Earth.

4. What is the difference between the sidereal and synodic months? What causes their different durations?

A synodic month is the period of time between two successive phases of the same name (for example, new moons), and it lasts 29.5 days.

A sidereal month is the period of the Moon's orbit around the Earth relative to the stars, and it lasts 27.3 days.

The different durations of these months are due to the fact that the Earth does not rest in one place, but moves in its orbit. Therefore, in order for the previous configuration to be repeated and the synodic month to end, the Moon has to travel a greater distance in its orbit than to complete the sidereal month.

5. What is meant by the lunar phase? Describe the phases of the moon.

The lunar phase is the part of the lunar disk visible in sunlight.

Let's look at the phases of the moon, starting with new moon. This phase occurs when the Moon passes between the Sun and the Earth and faces us with its dark side. The Moon is not visible at all from Earth. After one or two days, a narrow bright crescent appears in the western sky and continues to grow. "young" Moon. In 7 days the entire right half of the lunar disk will be visible - the first quarter phase. Then the phase increases, and 14-15 days after the new moon, the Moon comes into opposition with the Sun. Its phase becomes complete, comes full moon. The sun's rays illuminate the entire lunar hemisphere facing the Earth. After the full moon, the Moon gradually approaches the Sun from the west and is illuminated by it from the left. In about a week it comes last quarter phase. Then the new moon comes again...

6. The crescent of the Moon is convex to the right and close to the horizon. Which side of the horizon is it on?

The moon is observed in the western part of the horizon.

7. Why do solar and lunar eclipses occur?

As they move along their orbits, the Earth and Moon from time to time line up with the Sun. If the Moon is close to the plane of the Earth's orbit, an eclipse occurs. When the Moon comes between the Earth and the Sun, a solar eclipse occurs, and when the Earth comes between the Sun and the Moon, a lunar eclipse occurs.

8. Describe total, partial and annular solar eclipses.

Passing between the Sun and the Earth, the small Moon cannot completely obscure the Earth. The solar disk will be completely closed only to observers located inside the cone of the lunar shadow, the maximum diameter of which on the Earth's surface does not exceed 270 km. Only from here, from this relatively narrow area of ​​the earth's surface, where the shadow of the Moon falls, will it be possible to see total solar eclipse. In the same place where the penumbra of the Moon falls, inside the so-called lunar penumbra cone, it will be visible partial solar eclipse. If at the time of the eclipse the Moon, moving along its elliptical orbit, is located at a considerable distance from the Earth, then the visible disk of the Moon will be too small to completely cover the Sun. Then a shining rim of the solar disk will be observed around the dark disk of the Moon. This - annular eclipse.

Even in ancient times, astronomy helped people find their way. Simple techniques for determining direction in an unfamiliar place can still be useful to you today on a hike or a walk.
Direction to cardinal directions can be determined by the sun, moon and starseven more accurate than using a compass.

Sun orientation

To determine the cardinal directions by the sun, you can use ordinary . If you point the clock hand at the sun at one o'clock in the afternoon, it will show you the direction to the south, because the sun at noon is in the southern part of the sky. (Astronomical noon occurs around 1 p.m.). To determine the direction to the cardinal points at other times, you need to point the hour hand at the sun and divide the angle formed between this arrow and the number “1” in half. The resulting line will show the direction to the south. Before noon it will be located to the left of the number “1”, after noon - to the right (Fig. 1).
To more accurately point the hour hand at the sun, place a stick, such as a pencil, perpendicular to the plane of the clock in the center of the dial. Now turn the clock so that the shadow of the stick and the hour hand form a straight line. In this position, the hour hand will be pointing directly at the sun.

Orientation by the moon

At night and in the evening you can navigate by the moon. To do this, you need to know what the main phases of the moon look like.
There are four main phases of the moon.
New moon.The Moon is between the Earth and the Sun, at this time the shadow side of the Moon faces the Earth, and we do not see it.
First quarter.The moon is visible in the evening in the southwestern side of the sky in the form of a light semicircle, convexly facing to the right.

Full moon.The moon is completely illuminated and looks like a bright disk.
Last quarter.The moon is visible in the morning in the southeastern side of the sky in the form of a light semicircle, convexly facing to the left (Fig. 2).
You will find information about the onset of lunar phases in tear-off and table calendars, via the Internet.
To be able to navigate by the moon, you need to remember the following. The crescent of the “young” moon, curved to the right, is visible in the evening in the western sky and sets shortly after sunset. During the first quarter, the moon is in the south around 7 p.m. The full moon in the south direction occurs around 1 am. At 10 o'clock in the evening it is in the southeastern side of the sky, and at 4 o'clock in the morning it is in the southwest. The last quarter moon is in the south at 7 am. The crescent of the "old" moon, resembling the letter "C", is visible in the morning, shortly before sunrise, in the eastern sky. Knowing this, you can easily determine the points of the horizon based on the position of the moon and its phase.

Orientation by the stars

The moon is not always visible in the sky. But every night, when the sky is not covered with clouds, stars are visible on it, by which you can also determine the direction.
The easiest way to navigate is by the North Star, which always stands above the North Pole. The North Star is found in the constellation Ursa Major. This constellation is known to everyone and is visible throughout the night. The North Star is the end of the handle of the “bucket” of the constellation Ursa Minor.

Young or old month?

Seeing an incomplete disk of the Moon in the sky, not everyone can accurately determine whether it is a young month or whether it is already in decline. The narrow crescent of the newly born month and the crescent of the old Moon differ only in that they are convex in opposite directions. In the northern hemisphere, the young month is always directed with its convex side to the right, the old one - to the left. How to remember reliably and accurately which month is facing which way?

Let me offer this sign.

By the similarity of the sickle or crescent with the letters R or WITH it is easy to determine whether the month in front of us is growing (i.e. young) or old .

The French also have a mnemonic sign. They advise mentally attaching a straight line to the horns of the crescent moon; Latin letters are obtained d or r. Letter d – initial in the word “dernier” (last) - indicates the last quarter, i.e. the old month. Letter R - the initial in the word “premier” (first) indicates that the Moon is in the first quarter phase, generally young. The Germans also have a rule that associates the shape of the Moon with certain letters.

These rules can only be used in the northern hemisphere of the Earth. For Australia or the Transvaal the meaning will be just the opposite. But even in the northern hemisphere they may not be applicable - specifically in the southern latitudes.

Already in the Crimea and Transcaucasia, the sickle and crescent tilt strongly to one side, and even further south they lie completely flat. Near the equator, the crescent moon hanging on the horizon appears either as a gondola swinging on the waves (“the shuttle of the moon” in Arabian fairy tales) or as a light arch. Neither Russian nor French signs are suitable here - from a recumbent arch you can make both pairs of letters at will: R And S, r And d.

In order not to be mistaken about the age of the Moon in this case, one must turn to astronomical signs: the new moon is visible in the evening in the western part of the sky; old - in the morning in the eastern part of the sky.

Moon on flags

In Fig. 30 in front of us is the Turkish flag (former). It has an image of a crescent moon and a star. This leads us to the following questions:

1. Which month’s crescent is depicted on the flag – young or old?

2. Can the crescent moon and star be seen in the sky as they are shown on the flag?

Rice. 30. Flag of Turkey (former).

1. Remembering the sign just indicated and taking into account that the flag belongs to a country in the northern hemisphere, we establish that the month on the flag old.

Rice. 31. Why the star cannot be seen between the horns of the month

2. The star cannot be visible inside the disk of the Moon, completed to a circle (Fig. 31, A). All celestial bodies are much further than the Moon and, therefore, must be obscured by it. They can only be seen beyond the edge of the unlit part of the Moon, as shown in Fig. 31,6.

It is curious that on the modern flag of Turkey, which also contains an image of a lunar crescent and a star, the star is moved away from the crescent exactly as in Fig. 31, b.

Mysteries of the lunar phases

The Moon receives its light from the Sun, and therefore the convex side of the lunar crescents must, of course, be turned towards the Sun. Artists often forget about this. At painting exhibitions, it is not uncommon to see a landscape with a crescent moon facing the Sun with its straight side; there is also a lunar crescent turned towards the Sun with its horns (Fig. 32).

Rice. 32. An astronomical error was made on the landscape. Which? (Answer in text).

It should be noted, however, that drawing the new moon correctly is not as easy as it seems. Even experienced artists draw the outer and inner arcs of the crescent moon in the shape of semicircles (Fig. 33, b). Meanwhile, only the outer arc has a semicircular shape, while the inner one is a semi-ellipse, because it is a semicircle (the border of the illuminated part) visible in perspective (Fig. 33, A).

Rice. 33. How to (a) and how not to (b) depict a crescent moon

It is not easy to give the crescent moon its correct position in the sky. The crescent and crescent moon are often positioned in relation to the sun in a rather puzzling manner. It would seem that since the Moon is illuminated by the Sun, then the straight line connecting the ends of the month should make a right angle with the ray coming from the Sun to its middle (Fig. 34).

Rice. 34. Position of the lunar crescent relative to the Sun

In other words, the center of the Sun must be on a perpendicular drawn through the middle of the straight line connecting the ends of the month. However, this rule is observed only for a narrow crescent located near the Sun. In Fig. Figure 35 shows the position of the month in different phases relative to the rays of the Sun. The impression is as if the rays of the Sun are bent before reaching the Moon.

Rice. 35. In what position relative to the Sun do we see the Moon in different phases.

The answer lies in the following. The ray going from the Sun to the Moon is actually perpendicular to the line connecting the ends of the month, and in space it represents a straight line. But our eye draws not this straight line in the sky, but its projection onto the concave vault of the sky, that is, a curved line. This is why it seems to us that the Moon is “hung incorrectly” in the sky. The artist must study these features and be able to transfer them to the canvas.

Double planet

A double planet is the Earth and the Moon. They have the right to this name because our satellite stands out sharply among the satellites of other planets due to its significant size and mass in relation to its central planet. There are satellites in the solar system that are absolutely larger and heavier, but in comparison with their central planet they are much smaller than our Moon in relation to the Earth. In fact, the diameter of our Moon is more than a quarter of the Earth’s, and the diameter relative to the largest satellite of other planets is only a 10th of the diameter of its planet (Triton is a satellite of Neptune). Further, the Moon's mass is 1/81 that of the Earth; Meanwhile, the heaviest of the satellites that exists in the solar system, the III satellite of Jupiter, is less than 10,000th of the mass of its central planet.

The plate on page 86 shows what proportion of the mass of the central planet is the mass of large satellites. You can see from this comparison that our Moon, by its mass, makes up the largest share of its central planet.

The third thing that gives the Earth-Moon system the right to claim the name “double planet” is the close proximity of both celestial bodies. Many satellites of other planets orbit at much greater distances: some of Jupiter's satellites (for example, the ninth, Fig. 36) orbit 65 times further.

Rice. 36. The Earth-Moon system compared with the Jupiter system (the dimensions of the celestial bodies themselves are shown without scale)

In connection with this is the curious fact that the path described by the Moon around the Sun differs very little from the path of the Earth. This will seem incredible if you remember that the Moon moves around the Earth at a distance of almost 400,000 km. Let us not forget, however, that while the Moon makes one revolution around the Earth, the Earth itself manages to move along with it approximately the 13th part of its annual path, i.e. 70,000,000 km. Imagine the circular path of the Moon - 2,500,000 km - stretched along a distance 30 times greater. What will remain of its circular shape? Nothing. That is why the path of the Moon near the Sun almost merges with the Earth’s orbit, deviating from it only by 13 barely noticeable protrusions. It can be proven with a simple calculation (which we will not burden the exposition here) that the path of the Moon is everywhere directed towards its Sun concavity . Roughly speaking, it looks like a convex thirteen-sided triangle with softly rounded corners.

In Fig. 37 you see an accurate depiction of the paths of the Earth and Moon over the course of one month. The dotted line is the path of the Earth, the solid line is the path of the Moon. They are so close to each other that to depict them separately we had to take a very large drawing scale: the diameter of the earth’s orbit here is equal to? If we took 10 cm for it, then the greatest distance in the drawing between both paths would be less than the thickness of the lines depicting them. Looking at this drawing, you are clearly convinced that the Earth and the Moon move around the Sun almost along the same path and that the name double planet was assigned to them by astronomers quite rightly.

Rice. 37. Monthly path of the Moon (solid line) and the Earth (dashed line) around the Sun

So, to an observer placed on the Sun, the Moon's path would appear to be a slightly wavy line, almost coinciding with the Earth's orbit. This does not at all contradict the fact that in relation to the Earth the Moon moves along a small ellipse.

The reason, of course, is that, looking from the Earth, we do not notice the portable movement of the Moon along with the Earth in the Earth’s orbit, since we ourselves participate in it.

Why doesn't the Moon fall on the Sun?

The question may seem naive. Why on earth would the Moon fall on the Sun? After all, the Earth attracts it stronger than the distant Sun and, naturally, makes it revolve around itself.

Readers who think this way will be surprised to learn that the opposite is true: the Moon is more strongly attracted by the Sun, not by the Earth!

That this is so is shown by calculations. Let's compare the forces that attract the Moon: the force of the Sun and the force of the Earth. Both forces depend on two circumstances: on the magnitude of the attractive mass and on the distance of this mass from the Moon. The mass of the Sun is 330,000 times greater than the mass of the Earth; the Sun would attract the Moon the same number of times more strongly than the Earth if the distance to the Moon were the same in both cases.

But the Sun is about 400 times farther from the Moon than the Earth. The force of attraction decreases in proportion to the square of the distance; therefore, the attraction of the Sun must be reduced by 400 2, i.e., 160,000 times. This means that solar gravity is stronger than the earth’s by 330,000/160,000, i.e., more than two times.

So, the Moon is attracted by the Sun twice as much as by the Earth. Why then, in fact, does the Moon not fall on the Sun? Why does the Earth still force the Moon to revolve around it, rather than the action of the Sun taking over?

The Moon does not fall on the Sun for the same reason that the Earth does not fall on it; The Moon revolves around the Sun together with the Earth, and the attractive effect of the Sun is spent without a trace in order to constantly transfer both of these bodies from a straight path to a curved orbit, that is, to transform rectilinear motion into curvilinear one. Just take a look at Fig. 38 to verify what was said.

Some readers may still have some doubts. How does this come out anyway? The Earth pulls the Moon towards itself. The Sun pulls the Moon with greater force, and the Moon, instead of falling on the Sun, circles around the Earth? It would indeed be strange if the Sun attracted only the Moon. But it attracts the Moon together with the Earth, the entire “double planet,” and, so to speak, does not interfere with the internal relations of the members of this pair with each other. Strictly speaking, the common center of gravity of the Earth-Moon system is attracted to the Sun; This center (called the barycenter) revolves around the Sun under the influence of solar gravity. It is located at a distance of 2/3 of the Earth's radius from the center of the Earth towards the Moon. The Moon and the center of the Earth revolve around the barycenter, completing one rotation every month.

Visible and invisible sides of the Moon

Among the effects delivered by a stereoscope, nothing is as striking as the view of the Moon. Here you see with your own eyes that the Moon is really spherical, whereas in the real sky it appears flat, like a tea tray.

But how difficult it is to obtain such a stereoscopic photograph of our satellite, many do not even suspect. To make it, you need to be well acquainted with the peculiarities of the capricious movements of the night luminary.

The fact is that the Moon goes around the Earth in such a way that the same side faces it all the time. As it runs around the Earth, the Moon also rotates around its own axis, and both movements are completed in the same period of time.

In Fig. 38 you see an ellipse that should clearly depict the orbit of the Moon. The drawing deliberately enhances the elongation of the lunar ellipse; in fact, the eccentricity of the lunar orbit is 0.055 or 1/18. It is impossible to accurately represent the lunar orbit in a small drawing so that the eye can distinguish it from a circle: with the semi-major axis measuring even a whole meter, the semi-minor axis would be only 1 mm shorter than it; The earth would be only 5.5 cm away from the center. To make it easier to understand the further explanation, a more elongated ellipse is drawn in the figure.

Rice. 38. How the Moon moves around the Earth in its orbit (details in the text)

So, imagine that the ellipse in Fig. 38 is the path of the Moon around the Earth. The earth is placed at a point ABOUT - at one of the ellipse's foci. Kepler's laws apply not only to the movements of planets around the Sun, but also to the movements of satellites around the central planets, in particular to the revolution of the Moon. According to Kepler's second law, the Moon travels this distance in a quarter of a month. AE, what's the area OABCDE equals 1/4 the area of ​​the ellipse, i.e. the area MABCD(equal areas OAU And MAD in our drawing is confirmed by the approximate equality of areas MOQ And EQD). So, in a quarter of a month the Moon travels from A before E. The rotation of the Moon, like the rotation of planets in general, in contrast to their revolution around the Sun, occurs evenly: in 1/4 month it rotates exactly 90°. Therefore, when the Moon is in E, radius of the Moon facing the Earth at a point A, will describe an arc of 90°, and will not be directed towards a point M, and to some other point, to the left M, near another focus R lunar orbit. Because the Moon slightly turns its face away from the earthly observer, he will be able to see a narrow strip of its previously invisible half on the right side. At the point ELupa shows the earthly observer a narrower strip of its usually invisible side, because the angle OFP less angle OER. At the point G – at the apogee of the orbit - the Moon occupies the same position in relation to the Earth as at perigee A. As it moves further, the Moon turns away from the Earth in the opposite direction, showing our planet another strip of its invisible side: this strip first expands, then narrows, and at the point A The moon takes its previous position.

We are convinced that, due to the elliptical shape of the lunar path, our satellite does not face the Earth with exactly the same half. The Moon invariably faces the same side not to the Earth, but to another focus of its orbit. For us, it sways around the middle position like a scale; hence the astronomical name for this rocking: “libration” - from the Latin word “libra”, meaning “scales”. The amount of libration at each point is measured by the corresponding angle; for example, at the point is the libration is equal to the angle OER. The largest libration value is 7°53°, i.e. almost 8°.

It is interesting to watch how the libration angle increases and decreases as the Moon moves along its orbit. We'll put it in D the tip of the compass and describe the arc passing through the foci ABOUT And R. It will cross the orbit at points B and F. Angles OVR And OFP as inscribed equal to half the central angle ODP. From this we conclude that when the Moon moves from A before D libration grows quickly at first, at a point IN reaches half the maximum, then continues to increase slowly; on the way from D before F libration decreases slowly at first, then quickly. In the second half of the ellipse, libration changes its value at the same rate, but in the opposite direction. (The amount of libration at each point in the orbit is approximately proportional to the distance of the Moon from the major axis of the ellipse.)

That wobble of the Moon, which we have just examined, is called libration in longitude. Our satellite is also subject to another libration - in latitude. The plane of the lunar orbit is inclined to the plane of the Moon's equator by 6?°. Therefore, we see the Moon from the Earth in some cases a little from the south, in others from the north, looking a little into the “invisible” half of the Moon through its poles. This libration in latitude reaches 6?°.

Let us now explain how the astronomer-photographer uses the described slight swaying of the Moon around its middle position in order to obtain stereoscopic photographs of it. The reader probably guesses that for this it is necessary to lie in wait for two positions of the Moon in which in one it would be rotated relative to the other at a sufficient angle. At points A and B, B and C, C and D and etc. The Moon occupies such different positions in relation to the Earth that stereoscopic photographs are possible. But here we are faced with a new difficulty: in these positions, the difference in the age of the Moon, 1?-2 days, is too great, so that the strip of the lunar surface near the circle of illumination in one picture is already coming out of the shadow. This is unacceptable for stereoscopic images (the strip will shine like silver). A difficult task arises: to lie in wait for identical phases of the Moon, which differ in the magnitude of libration (in longitude) so that the circle of illumination passes over the same parts of the lunar surface. But this is not enough: in both positions there must also be equal librations in latitude.

Our reader is unlikely to take lunar stereo photographs. The method of obtaining them is explained here, of course, not for a practical purpose, but only in order to consider the features of the lunar movement, which give astronomers the opportunity to see a small strip of the side of our satellite usually inaccessible to the observer. Thanks to both lunar librations, we see, in general, not half of the entire lunar surface, but 59% of it. Before the launch of the third space rocket towards the Moon in the Soviet Union, 41% of the lunar surface was inaccessible to study.

No one knew how this part of the lunar surface was structured. Ingenious attempts were made, by continuing back parts of the lunar ridges and light stripes passing from the invisible part of the Moon to the visible, to sketch out some details of the half inaccessible to us. As a result of the launch of the automatic interplanetary station “Luna-3” on October 4, 1959, photographs of the far side of the Moon were obtained. Soviet scientists received the right to name the newly discovered lunar formations. The craters are named after prominent figures of science and culture - Lomonosov, Tsiolkovsky, Joliot-Curie and others, and two new seas are named - the Sea of ​​Moscow and the Sea of ​​Dreams. The far side of the Moon was photographed for the second time by the Soviet probe Zond-3, launched on July 18, 1965.

In 1966, Luna 9 softly landed on the moon and transmitted an image of the lunar landscape to Earth. In 1969, the lunar Sea of ​​Tranquility experienced trouble. The landing cabin of the American spacecraft Apollo 11 sank to the dry bottom of this “sea.” Astronauts Neil Armstrong and Edwin Aldrin became the first humans to set foot on the Moon. They installed several instruments, took samples of lunar soil and returned to the ship that was waiting for them in orbit. Apollo 11 was piloted by Michael Collins. By the end of 1972, five more American expeditions had visited the Moon.

At the same time, automatic stations were launched to the Moon in the USSR. In 1970, Luna 16, descending on the surface of the Moon, took samples of lunar soil for the first time and delivered them to Earth. In the same year, Luna-17 launched the self-propelled Lunokhod-1 onto the surface of our satellite. This eight-wheeled robot, which looks like both a turtle and an army field kitchen, covered almost 11 kilometers in 301 days and transmitted 20,000 images, 200 panoramas to Earth and carried out soil research at 500 points.

A little later, Luna 20 brought back to Earth soil samples from the mountainous region of the Moon, inaccessible to astronauts. In 1973, Luna-21 sent Lunokhod-2 on a mission, which covered 37 km in 4.5 months, exploring the terrain and soil composition. Both wheeled robots were controlled from the Earth by radio and systematically transmitted pictures of lunar landscapes and soil analysis results to the control center. The Luna-24 automatic station (1976) drilled lunar soil to a depth of 2 m and delivered 170 g of its samples to Earth.

The often expressed idea about the existence of an atmosphere and water on the far side of the Moon is unfounded and contradicts the laws of physics: if there is no atmosphere and water on one side of the Moon, then there cannot be them on the other (we will return to this issue).

Second Moon and Lunar Moon

From time to time, reports appear in the press that one or another observer managed to see the second satellite of the Earth, its second Moon.

The question of the existence of a second satellite of the Earth is not new. It has a long history behind it. Anyone who has read Jules Verne’s novel “From a Gun to the Moon” probably remembers that the second Moon is already mentioned there. It is so small and its speed is so great that the inhabitants of the Earth cannot observe it. The French astronomer Petit, says Jules Bern, suspected its existence and determined the period of its revolution around the Earth at 3 hours 20 m. Its distance from the surface of the Earth is 8140 km. It is curious that the English magazine “Knowledge”, in an article about astronomy by Jules Verne, considers the reference to Petit, as well as Petit himself, to be simply fictitious. There is really no mention of this astronomer in any encyclopedia. And yet the novelist’s message is not fictitious. The director of the Toulouse Observatory, Petit, in the 50s of the last century really defended the existence of a second Moon - a meteorite with an orbital period of 3 hours 20 m, circling, however, not 8,000, but 5,000 km from the earth’s surface. This opinion was shared even then by only a few astronomers, and was subsequently completely forgotten. Theoretically, there is nothing unscientific in assuming the existence of a second, very small satellite of the Earth. But such a celestial body should be observed not only in those rare moments when it passes (apparently) across the disk of the Moon or the Sun. Even if it turns so close to the Earth that with each rotation it must plunge into the wide earth's shadow, then even in this case it would be possible to see it in the morning and evening sky shining as a bright star in the rays of the Sun. With its rapid movement and frequent returns, this star would attract the attention of many observers. At the moments of a total solar eclipse, the second Moon would also not escape the gaze of astronomers. In a word, if the Earth really had a second satellite, it would happen to be observed quite often. Meanwhile, there were not a single indisputable observations.

Strictly speaking, the Earth has, in addition to the Moon, two more satellites. Not artificial, but completely natural. And not tiny, but the same size as the Moon itself. But, although these “Moons” were discovered a long time ago (in 1956, by the Polish astronomer Kordylewski), very few people managed to see them. The thing is that these satellites consist entirely of dust. These dusty “Moons” move among the stars along the same path as the real Moon, and at the same speed. One is 60 degrees ahead of the Moon, the other is the same amount behind. And they are separated from the Earth by the same distance as the Moon. The edges of these "Moons" are blurred, making observation very difficult.

Along with the problem of the second Moon, the question was also raised about whether our Moon has its own small satellite - the “moon of the Moon”.

But it is very difficult to directly verify the existence of such a lunar satellite. Astronomer Multon expresses the following considerations about this:

“When the Moon shines with full light, its light or the light of the Sun does not make it possible to distinguish a very small body in its vicinity. Only at the moments of lunar eclipses could the Moon's satellite be illuminated by the Sun, while neighboring areas of the sky would be free from the influence of the scattered light of the Moon. Thus, only during lunar eclipses could one hope to discover a small body orbiting the Moon. This kind of research has already been carried out, but did not produce real results.”

Why does the Moon have no atmosphere?

This question belongs to those that become clearer if you first turn them over, so to speak. Before we talk about why the Moon does not retain an atmosphere around itself, let us pose the question: why does it retain an atmosphere around our own planet? Let us remember that air, like any gas, is a chaos of unconnected molecules rapidly moving in different directions. Their average speed at t = 0 °C – about? km per second (gun bullet speed). Why don’t they scatter into outer space? For the same reason that a rifle bullet does not fly into outer space. Having exhausted the energy of their movement to overcome the force of gravity, the molecules fall back to Earth. Imagine a molecule near the earth's surface flying vertically upward at speed? km per second. How high can she fly? It is easy to calculate: speed v, lift height h and gravity acceleration g are related by the following formula:

v 2 = 2gh.

Let's substitute instead of v its value - 500 m/s, instead of g – 10 m/s 2, we have

h = 12,500 m = 12? km.

But if air molecules cannot fly above 12? km, then where do air molecules above this boundary come from? After all, the oxygen that makes up our atmosphere was formed near the earth’s surface (from carbon dioxide as a result of plant activity). What force lifted and holds them at an altitude of 500 kilometers or more, where the presence of traces of air has certainly been established? Physics gives here the same answer that we would hear from a statistician if we asked him: “The average duration of human life is 70 years; Where do 80-year-old people come from?” The thing is that the calculation we performed refers to an average, and not a real molecule. The average molecule has a second speed of? km, but real molecules move some more slowly, others faster than average. True, the percentage of molecules whose speed noticeably deviates from the average is small and quickly decreases as the magnitude of this deviation increases. Of the total number of molecules contained in a given volume of oxygen at 0°, only 20% have a speed of 400 to 500 m per second; approximately the same number of molecules move at a speed of 300–400 m/s, 17% – at a speed of 200–300 m/s, 9% – at a speed of 600–700 m/s, 8% – at a speed of 700–800 m/s, 1% – at a speed of 1300–1400 m/s. A small part (less than a millionth part) of molecules has a speed of 3500 m/s, and this speed is sufficient for the molecules to fly even to a height of 600 km.

Really, 3500 2 = 20h, where h=12250000/20 i.e. over 600 km.

The presence of oxygen particles at an altitude of hundreds of kilometers above the earth's surface becomes clear: this follows from the physical properties of gases. The molecules of oxygen, nitrogen, water vapor, and carbon dioxide, however, do not possess speeds that would allow them to completely leave the globe. This requires a speed of at least 11 km per second, and only single molecules of these gases have such speeds at low temperatures. This is why the Earth holds its atmospheric shell so tightly. It has been calculated that for the loss of half the supply of even the lightest of the gases in the earth's atmosphere - hydrogen - a number of years must pass, expressed in 25 digits. Millions of years will not make any change in the composition and mass of the earth's atmosphere.

To explain now why the Moon cannot maintain a similar atmosphere around itself, it remains to say a little.

The gravitational pull on the Moon is six times weaker than on Earth; Accordingly, the speed required to overcome the force of gravity there is also less and equal to only 2360 m/s. And since the speed of oxygen and nitrogen molecules at moderate temperatures can exceed this value, it is clear that the Moon would have to continuously lose its atmosphere if it were to form one.

When the fastest of the molecules evaporate, other molecules will acquire a critical speed (this is a consequence of the law of distribution of velocities between gas particles), and more and more new particles of the atmospheric shell must irrevocably escape into outer space.

After a sufficient period of time, insignificant on the scale of the universe, the entire atmosphere will leave the surface of such a weakly attractive celestial body.

It can be proven mathematically that if the average speed of molecules in the atmosphere of a planet is even three times less than the maximum (i.e., for the Moon it is 2360: 3 = 790 m/s), then such an atmosphere should dissipate by half within a few weeks. (The atmosphere of a celestial body can be stably preserved only if the average speed of its molecules is less than one-fifth of the maximum speed.) It has been suggested—or rather, a dream—that over time, when earthly humanity visits and conquers the Moon, it will surround it with an artificial atmosphere and thus make it suitable for habitation. After what has been said, the unrealizability of such an enterprise should be clear to the reader.

The absence of an atmosphere on our satellite is not an accident, not a whim of nature, but a natural consequence of physical laws.

It is also clear that the reasons why the existence of an atmosphere on the Moon is impossible should determine its absence in general on all world bodies with weak gravity: on asteroids and on most planetary satellites.

Dimensions of the lunar world

This, of course, is clearly indicated by numerical data: the diameter of the Moon (3500 km), surface, volume. But numbers, which are indispensable in calculations, are powerless to give that visual representation of the sizes that our imagination requires. It will be useful to turn to specific comparisons for this.

Let's compare the lunar continent (after all, the Moon is a solid continent) with the continents of the globe (Fig. 39). This will tell us more than the abstract statement that the total surface of the lunar globe is 14 times smaller than the earth's surface. In terms of the number of square kilometers, the surface of our satellite is only slightly smaller than the surface of the Americas. And that part of the Moon that faces the Earth and is accessible to our observation is almost exactly equal to the area of ​​South America.

Rice. 39. The size of the Moon compared to the continent of Europa (one should not, however, conclude that the surface of the lunar globe is smaller than the surface of Europa)

To make clear the size of the lunar “seas” in comparison with the terrestrial ones, in Fig. 40 on the map of the Moon the contours of the Black and Caspian Seas are superimposed on the same scale. It is immediately clear that the lunar “seas” are not particularly large, although they occupy a noticeable part of the disk. Sea of ​​Clarity, for example (170,000 km 2 ), approximately in 2? times less than the Caspian.

But among the ring mountains of the Moon there are genuine giants, which do not exist on Earth. For example, the circular shaft of Mount Grimaldi covers a surface larger than the area of ​​Lake Baikal. A small state, such as Belgium or Switzerland, could fit entirely inside this mountain.

Rice. 40. Earth's seas compared to lunar ones. The Black and Caspian Seas, transferred to the Moon, would be there larger than all the lunar seas (the numbers indicate: 1 – Sea of ​​Rains, 2 – Sea of ​​Clarity, 3 – Sea of ​​Tranquility, 4 – Sea of ​​Abundance, 5 – Sea of ​​Nectar)

Lunar landscapes

Photographs of the lunar surface are reproduced in books so often that the appearance of the characteristic features of the lunar relief - ring mountains (Fig. 41), "craters" - is probably familiar to each of our readers. It is possible that others observed the lunar mountains through a small pipe; A tube with a 3 cm lens is sufficient for this.

Rice. 41. Typical ring mountains of the Moon

But neither photographs nor observations through a telescope give any idea of ​​what the lunar surface would look like to an observer on the Moon itself. Standing directly next to the lunar mountains, an observer would see them from a different perspective than through a telescope. It’s one thing to look at an object from a great height and quite another to look at it from the side close up. Let us show with several examples how this difference manifests itself. Mount Eratosthenes appears from Earth as a ring shaft with a peak inside. Through a telescope, it appears bold and sharp thanks to clear, unblurred shadows. Take a look, however, at its profile (Fig. 42): you see that compared to the huge diameter of the crater - 60 km - the height of the shaft and the inner cone is very small; The gentleness of the slopes further conceals their height.

Rice. 42. Profile of the Great Ring Mountain

Imagine yourself now wandering inside this crater and remember that its diameter is equal to the distance from Lake Ladoga to the Gulf of Finland. You will then hardly catch the ring-shaped shape of the shaft; in addition, the convexity of the soil will hide its lower part from you, since the lunar horizon is twice as narrow as the earth’s (corresponding to four times the smaller diameter of the lunar globe). On Earth, a person of average height, standing on level ground, can see around him no further than 5 km. This follows from the horizon range formula

Where D – range in km, h – eye height in km, R – radius of the planet in km.

Substituting the data for the Earth and the Moon into it, we find out that for a person of average height the horizon distance is

on Earth………,4.8 km,

on the Moon……….2.5 km.

What picture would appear to an observer inside a large lunar crater is shown in Fig. 43. (The landscape is depicted for another large crater - Archimedes.) Isn’t it true: a vast plain with a chain of hills on the horizon bears little resemblance to what is usually imagined when the words “lunar crater” are said?

Rice. 43. What picture would an observer see if he stood in the center of a large ring mountain on the Moon.

Finding himself on the other side of the shaft, outside the crater, the observer would also see something different from what he expected. The outer slope of the ring mountain (cf. Fig. 42) rises so gently that the traveler will not see it as a mountain at all, and most importantly, he will not be able to be convinced that the hilly ridge he sees is a ring mountain with a round basin. To do this, you will have to cross its crest, and even here, as we have already explained, nothing remarkable awaits the lunar climber.

In addition to the huge ring lunar mountains, there are, however, many small craters on the Moon that are easy to see, even standing in close proximity. But their height is insignificant; the observer is unlikely to be struck by anything unusual here. But the lunar mountain ranges, which bear the names of terrestrial mountains: the Alps, the Caucasus, the Apennines, etc., compete with the terrestrial ones in height and reach 7–8 km. On the relatively small Moon they look quite impressive.

Rice. 44. Half a pea casts a long shadow in oblique lighting

The absence of an atmosphere on the Moon and the associated sharpness of the shadows create a curious illusion when observed through a telescope: the slightest irregularities in the soil are magnified and appear very prominent. Place half of the pea with the bulge facing up. Is it big? And look what a long shadow it casts (Fig. 44). With side lighting on the Moon, the shadow is 20 times greater than the height of the body that casts it, and this has served astronomers in good stead: thanks to long shadows, objects 30 m high can be observed through a telescope on the Moon. But the same circumstance forces us to exaggerate the unevenness of the lunar surface. soil. Mount Pico, for example, is outlined so sharply through a telescope that you can’t help but imagine it as a sharp and steep rock (Fig. 45). This is how she was portrayed in the past. But, observing it from the lunar surface, you would see a completely different picture - what is shown in Fig. 46.

But other features of the lunar relief, on the contrary, are underestimated by us. Through a telescope, we observe thin, barely noticeable cracks on the surface of the Moon, and it seems to us that they cannot play a significant role in the lunar landscape.

Rice. 45. Mount Pico used to be considered steep and sharp

Rice. 46. ​​In fact, Mount Pico has very gentle slopes.

Rice. 47. The so-called “Straight Wall” on the Moon; telescope view

But transported to the surface of our satellite, we would see in these places at our feet a deep black abyss stretching far beyond the horizon. Another example. There is a so-called “Straight Wall” on the Moon - a sheer ledge cutting through one of its plains. Seeing this wall through a telescope (Fig. 47), we forget that it is 300 m high; standing at the base of the wall, we would be overwhelmed by its enormity. In Fig. 48 the artist tried to depict this sheer wall, visible from below: its end is lost somewhere beyond the horizon: after all, it stretches for 100 km! In the same way, thin cracks, visible through a strong telescope on the lunar surface, should in reality represent huge failures (Fig. 49).

Rice. 48. What a “Straight Wall” should appear to an observer located near its base

Rice. 49. One of the lunar “cracks” observed in close proximity.

Moonlit sky

Black firmament

If an inhabitant of the Earth could find himself on the Moon, three extraordinary circumstances would attract his attention before others.

The strange color of the daytime sky on the Moon would immediately catch your eye: instead of the usual blue dome, there would be a completely black sky dotted with the bright shine of the Sun! - a lot of stars, clearly visible, but not twinkling at all. The reason for this phenomenon is the absence of an atmosphere on the Moon.

“The blue vault of a clear and pure sky,” says Flammarion in his characteristic picturesque language, “the gentle blush of dawn, the majestic glow of evening twilight, the enchanting beauty of deserts, the foggy distance of fields and meadows, and you, the mirror waters of lakes, since ancient times reflecting the distant azure skies , containing the whole infinity in their depths - your existence and all your beauty depend exclusively on that light shell that extends over the globe. Without her, none of these paintings, none of these lush colors would exist. Instead of an azure blue sky, you would be surrounded by endless black space; instead of majestic sunrises and sunsets, days would abruptly, without transitions, give way to nights and nights to days. Instead of the gentle half-light that reigns everywhere where the dazzling rays of the Sun do not directly fall, there would be bright light only in places directly illuminated by the daylight, and in all the rest there would be thick shadow.”

Earth in the sky of the moon

The second attraction on the Moon is the huge disk of the Earth hanging in the sky. It will seem strange to the traveler that the globe that was left behind when flying to the Moon at the bottom , suddenly found myself here up .

There is no one top and bottom in the universe for all the worlds, and it should not surprise you that, if you left the Earth below, you would see it above while on the Moon.

The disk of the Earth hanging in the lunar sky is huge: its diameter is approximately four times larger than the diameter of the familiar lunar disk in the earth’s sky. This is the third amazing fact that awaits the lunar traveler. If on lunar nights our landscapes are quite well lit, then nights on the Moon, with the rays of the full Earth with a disk 14 times larger than the lunar one, should be unusually light. The brightness of a star depends not only on its diameter, but also on the reflectivity of its surface. In this respect, the earth's surface is six times larger than the moon's; therefore, the light of a full Earth should illuminate the Moon 90 times more powerfully than a full month illuminates the Earth. On “earthly nights” on the Moon it would be possible to read fine print. The illumination of the lunar soil by the Earth is so bright that it allows us, from a distance of 400,000 km, to distinguish the night part of the lunar globe in the form of a vague flickering inside a narrow crescent; it is called the “ash light” of the Moon. Imagine 90 full moons pouring their light from the sky, and also take into account the absence of an atmosphere on our satellite that absorbs part of the light, and you will get some idea of ​​​​the enchanting picture of lunar landscapes, flooded in the middle of the night with the radiance of the full Earth.

Could a lunar observer be able to discern the outlines of continents and oceans on the Earth's disk? It is a common misconception that the Earth in the Moon's sky represents something similar to a school globe. This is how artists depict it when they have to draw the globe in world space: with the contours of the continents, with a snow cap in the polar regions, and other details. All this must be attributed to the realm of fantasy. On the globe, when observed from the outside, such details cannot be distinguished. Not to mention the clouds, which usually cover half of the earth's surface, our atmosphere itself strongly scatters the sun's rays; therefore the Earth should appear as bright and as opaque to the eye as Venus. Pulkovo astronomer G.A., who studied this issue. Tikhov wrote:

“Looking at the Earth from space, we would see a disk the color of a very whitish sky and would hardly discern any details of the surface itself. A significant portion of the sunlight falling on the Earth manages to be scattered in space by the atmosphere and all its impurities before it reaches the surface of the Earth itself. And what is reflected by the surface itself will again have time to weaken greatly due to new scattering in the atmosphere.”

So, while the Moon clearly shows us all the details of its surface, the Earth hides its face from the Moon, and indeed from the entire universe, under a shining blanket of the atmosphere.

But this is not the only difference between the lunar night luminary and the earthly one. In our sky, the month rises and sets, describing its path along with the star dome. In the lunar sky, the Earth does not make such a movement. She does not rise or set there, does not take part in the orderly, extremely slow procession of the stars. It hangs almost motionless in the sky, occupying a certain position for each point of the Moon, while the stars slowly glide behind it. This is a consequence of the feature of lunar motion that we have already considered, which is that the Moon always faces the Earth with the same part of its surface. For a lunar observer, the Earth hangs almost motionless in the vault of heaven. If the Earth stands at the zenith of some lunar crater, then it never leaves its zenith position. If from some point it is visible on the horizon, it forever remains on the horizon of that place. Only lunar librations, which we have already discussed, somewhat disturb this immobility. The starry sky makes its slow rotation behind the earth's disk, at 27 1/3 of our day; the Sun goes around the sky at 29? days, the planets make similar movements, and only one Earth rests almost motionless in the black sky.

But, remaining in one place, the Earth quickly, every 24 hours, rotates around its axis, and if our atmosphere were transparent, the Earth could serve as the most convenient celestial clock for future passengers of interplanetary spacecraft. In addition, the Earth has the same phases as the Moon shows in our sky. This means that our world does not always shine in the lunar sky as a full disk: it appears sometimes in the form of a semicircle, sometimes in the form of a sickle, more or less narrow, sometimes in the form of an incomplete circle, depending on what part of the half of the Earth illuminated by the Sun is facing the Moon. By drawing the relative positions of the Sun, Earth and Moon, you can easily see that the Earth and Moon should show opposite phases to each other.

When we observe a new moon, a lunar observer should see the full disk of the Earth - a “full Earth”; on the contrary, when we have a full moon, there is “new earth” on the moon (Fig. 50). When we see the narrow crescent of the new month, from the Moon we could admire the Earth in its demise, and the full disk is missing just such a crescent as the Moon shows us at that moment. However, the phases of the Earth are not as sharply defined as the lunar ones: the Earth’s atmosphere blurs the boundary of light, creating that gradual transition from day to night and back, which we observe on Earth in the form of twilight.

Rice. 50. “New Earth” on the Moon. The black disk of the Earth is surrounded by a bright border of the Earth's shining atmosphere

Another difference between the earth's phases and the lunar phases is as follows. On Earth, we never see the Moon at the very moment of the new moon. Although it usually stands above or below the Sun (sometimes by 5°, i.e. 10 of its diameters), so that the narrow edge of the lunar globe illuminated by the Sun could be visible, it is still inaccessible to our vision: the brilliance of the Sun beats out the modest radiance of the silver thread of the new moon. We usually notice the new Moon only at the age of two days, when it has time to move a sufficient distance from the Sun, and only in rare cases (in spring) - at the age of one day. This is not the case when observing “new earth” from the Moon: there is no atmosphere there, scattering a shining halo around the daylight. Stars and planets are not lost there in the rays of the Sun, but clearly stand out in the sky in the immediate vicinity of it. Therefore, when the Earth is not directly in front of the Sun (i.e., not during eclipses), but slightly above or below it, it is always visible in the black, star-studded sky of our satellite in the shape of a thin sickle with horns facing away from the Sun (Fig. .51). As it moves away from the Earth to the left of the Sun, the sickle seems to roll to the right.

Rice. 51. “Young” Earth in the sky of the Moon. The white circle under the earth's sickle is the Sun

A phenomenon corresponding to the one just described can be seen by observing the Moon through a small telescope: on a full moon, the disk of the night star is not seen by us in the form of a complete circle; since the centers of the Moon and the Sun do not lie on the same straight line with the observer’s eye, the lunar disk lacks a narrow crescent, which slides as a dark strip near the edge of the illuminated disk to the left as the Moon moves to the right. But the Earth and Moon always show opposite phases to each other; therefore, at the moment described, the lunar observer should have seen a thin crescent of “new earth”.

Rice. 52. Slow movements of the Earth near the lunar horizon due to libration. Dashed lines - the path of the center of the earth's disk

We have already noticed in passing that the librations of the Moon should affect the fact that the Earth is not completely motionless in the lunar sky: it fluctuates around its average position in the north-south direction by 14°, and in the west-east by 16°. For those points of the Moon where the Earth is visible on the very horizon, our planet should therefore sometimes appear to be setting and soon then rising again, describing strange curves (Fig. 52). This kind of sunrise or sunset of the Earth in one place on the horizon, without going around the entire sky, can last many Earth days.

Eclipses on the Moon

Let us supplement the picture of the lunar sky sketched now with a description of those celestial spectacles called eclipses. There are two types of eclipses on the Moon: solar and “terrestrial”. The first are not similar to the solar eclipses we are familiar with, but are extremely spectacular in their own way. They occur on the Moon at those moments when there are lunar eclipses on Earth, since then the Earth is placed on the line connecting the centers of the Sun and the Moon. At these moments our satellite plunges into the shadow cast by the globe. Anyone who has happened to see the Moon at such moments knows that it is not completely deprived of light, does not disappear from the eye; it is usually visible in cherry-red rays penetrating inside the cone of the earth's shadow. If we were transported at this moment to the surface of the Moon and looked from there at the Earth, we would clearly understand the reason for the red illumination: in the sky of the Moon, the globe, placed in front of the bright, although much smaller Sun, appears as a black disk surrounded by a crimson border of its atmosphere. It is this border that illuminates the Moon, immersed in the shadow, with a reddish light (Fig. 53).

Rice. 53. Progress of a solar eclipse on the Moon: The Sun C gradually sets behind the earth’s disk 3, hanging motionless in the lunar sky.

Solar eclipses on the Moon last not a few minutes, as on Earth, but more than 4 hours - as long as our lunar eclipses, because, in essence, these are our lunar eclipses, only observed not from the Earth, but from the Moon.

As for “earthly” eclipses, they are so insignificant that they barely deserve the name eclipses. They occur at those moments when solar eclipses are visible on Earth. On the large disk of the Earth, lunar observers would then see a small moving black circle - these are happy areas of the earth's surface from where they can admire the eclipse of the Sun.

It should be noted that eclipses such as our solar ones cannot be observed anywhere else in the planetary system. We owe this exceptional spectacle to an accidental circumstance: the Moon, blocking the Sun from us, is exactly as many times closer to us than the Sun, how many times the lunar diameter is smaller than the solar one - a coincidence that is not repeated on any other planet.

Why do astronomers observe eclipses?

Thanks to the now noted accident, the long cone of the shadow, which our satellite constantly drags behind it, reaches just to the earth’s surface (Fig. 54). As a matter of fact, the average length of the lunar shadow cone is less than the average distance of the Moon from the Earth, and if we were dealing only with average values, we would come to the conclusion that we never experience total solar eclipses. They actually happen because the Moon moves around the Earth in an ellipse and in some parts of the orbit it is 42,200 km closer to the Earth's surface than in others: the distance of the Moon varies from 363,300 to 405,500 km.

Rice. 54. The end of the cone of the moon's shadow slides along the earth's surface; in places covered by it a solar eclipse is observed

Sliding along the earth's surface, the end of the lunar shadow draws on it the “line of visibility of a solar eclipse.” This strip is no wider than 300 km, so the number of populated areas that are rewarded with the spectacle of a solar eclipse is quite limited each time. If we add to this that the duration of a total solar eclipse is calculated in minutes (no more than eight), then it becomes clear that a total solar eclipse is an extremely rare spectacle. For any given point on the globe, it happens once every two or three centuries.

Scientists therefore literally hunt for solar eclipses, equipping special expeditions to those, sometimes very remote for them, places on the globe from where this phenomenon can be observed. The 1936 solar eclipse (June 19) was visible as total only within the Soviet Union, and 70 foreign scientists from ten different countries came to us to observe it for two minutes. At the same time, the efforts of four expeditions were wasted due to cloudy weather. The scope of work by Soviet astronomers to observe this eclipse was extremely large. About 30 Soviet expeditions were sent to the total eclipse.

In 1941, despite the war, the Soviet government organized a number of expeditions located along the total eclipse strip from the Sea of ​​Azov to Almaty. And in 1947, a Soviet expedition went to Brazil to observe the total eclipse on May 20. Observations of solar eclipses on February 25, 1952, June 30, 1954, and February 15, 1961 took on a particularly large scale in the USSR. On May 30, 1965, a Soviet expedition observed an eclipse on the tiny island of Manuae in the southwestern part of the Pacific Ocean.

Although lunar eclipses occur one and a half times less frequently than solar eclipses, they are observed much more often. This astronomical paradox is explained very simply.

A solar eclipse can be observed on our planet only in a limited zone for which the Sun is obscured by the Moon; within this narrow strip it is complete for some points, and partial for others (i.e. the Sun is only partially obscured). The moment of the onset of a solar eclipse is also different for different points of the strip, not because there is a difference in the calculation of time, but because the lunar shadow moves along the earth's surface and different points are covered by it at different times.

A lunar eclipse proceeds completely differently. It is observed immediately over the entire half of the globe, where at this time the Moon is visible, that is, it is above the horizon.

Successive phases of a lunar eclipse occur for all points on the earth's surface at the same moment; the difference is due only to the difference in timing.

This is why the astronomer does not need to “hunt” for lunar eclipses: they come to him on their own. But in order to “catch” a solar eclipse, you sometimes have to travel very far. Astronomers send expeditions to tropical islands, far to the west or east, just to observe the covering of the solar disk by the black circle of the Moon for a few minutes.

Does it make sense to equip expensive expeditions for such fleeting observations? Is it not possible to make the same observations without waiting for the Moon to accidentally obscure the Sun? Why don’t astronomers produce a solar eclipse artificially by obscuring the image of the Sun in a telescope with an opaque circle? Then it would be possible, it would seem, to observe without hassle those surroundings of the Sun that astronomers are so interested in during eclipses.

Such an artificial solar eclipse cannot, however, produce what is observed when the Sun is obscured by the Moon. The fact is that the rays of the Sun, before reaching our eyes, pass through the earth's atmosphere and are scattered here by air particles. That is why the sky during the day appears to us as a light blue vault, and not black, dotted with stars, as it would appear to us even during the day in the absence of an atmosphere. By covering the Sun with a circle, but remaining at the bottom of the ocean of air, although we protect the eye from the direct rays of the daylight, the atmosphere above us is still flooded with sunlight and continues to scatter the rays, eclipsing the stars. This does not happen if the obscuring screen is outside the atmosphere. The Moon is just such a screen, located a hundred times further than the tangible boundary of the atmosphere. The sun's rays are delayed by this screen before they penetrate the earth's atmosphere, and therefore there is no scattering of light in the shaded strip. True, not completely: few rays penetrate into the shadow area, scattered by the surrounding light areas, and therefore the sky at the moment of a total solar eclipse is never as black as at midnight; Only the brightest stars are visible.

What tasks do astronomers set themselves when observing a total solar eclipse? Let us note the main ones.

The first is the observation of the so-called “reversal” of spectral lines in the outer shell of the Sun. The lines of the solar spectrum, which under normal conditions are dark on a light strip of the spectrum, become light for a few seconds on a dark background after the moment of complete coverage of the Sun by the disk of the Moon: the absorption spectrum turns into an emission spectrum. This is the so-called “flash spectrum”. Although this phenomenon, which provides precious material for judging the nature of the outer shell of the Sun, can, under certain conditions, be observed not only during an eclipse, it is detected so clearly during eclipses that astronomers strive not to miss such an opportunity.

Rice. 55. At the moment of a total solar eclipse, the “solar corona” flares up around the black disk of the Moon

The second task is research. solar corona . The corona is the most remarkable of the phenomena observed at the moments of a total solar eclipse: around the completely black circle of the Moon, bordered by fiery protrusions (prominences) of the outer shell of the Sun, a pearl halo of various sizes and shapes shines at different eclipses (Fig. 55). The long rays of this radiance are often several times larger than the solar diameter, and the brightness is usually only half the brightness of the full Moon.

During the 1936 eclipse, the solar corona was exceptionally bright, brighter than the full Moon, which rarely happens. The long, somewhat blurry rays of the corona extended over three or more solar diameters; the entire crown appeared in the form of a five-pointed star, the center of which was occupied by the dark disk of the Moon.

During eclipses, astronomers photograph the corona, measure its brightness, and study its spectrum. All this helps to study its physical structure.

Rice. 56. One of the consequences of the general theory of relativity is the deflection of light rays under the influence of the gravitational force of the Sun. According to the theory of relativity, an earthly observer at G sees a star at point E in the direction of the straight line TDFE, while in reality the star is at point E and sends its rays along the curved path EBFDT. In the absence of the Sun, the light beam from the star is to the Earth T would be directed in a straight line

The third task, put forward only in recent decades, is to test one of the consequences of the general theory of relativity. According to the theory of relativity, the rays of stars, passing by the Sun, are influenced by its powerful attraction and undergo a deflection, which should be revealed in the apparent displacement of stars near the solar disk (Fig. 56). Verification of this consequence is possible only during a total solar eclipse.

Measurements during the eclipses of 1919, 1922, 1926 and 1936. did not give, strictly speaking, decisive results, and the question of experimental confirmation of the indicated consequence from the theory of relativity remains open to this day.

These are the main reasons for which astronomers leave their observatories and go to remote, sometimes very inhospitable places to observe solar eclipses.

As for the picture of a total solar eclipse itself, in our fiction there is an excellent description of this rare natural phenomenon (V.G. Korolenko “At the Eclipse”; the description refers to the eclipse in August 1887; the observation was made on the banks of the Volga, in the city of Yuryevets .) Here is an excerpt from Korolenko’s story with minor omissions:

“The sun sinks for a minute in a wide, hazy spot and appears from the cloud already significantly damaged...

Now this is visible to the naked eye, helped by the thin steam that still smokes in the air, softening the dazzling shine.

Silence. Here and there you can hear nervous, heavy breathing...

Half an hour passes. The day shines almost the same, the clouds cover and reveal the sun, now floating above in the shape of a sickle.

There is a carefree excitement and curiosity among the youth.

Old men sigh, old women somehow groan hysterically, and some even scream and moan, as if from a toothache.

The day begins to noticeably turn pale. People's faces take on a frightened hue, the shadows of human figures lie on the ground, pale and unclear. The steamboat going down floats by as some kind of ghost. Its outlines became lighter and lost the definition of colors. The amount of light is apparently decreasing, but since there are no condensed shadows of the evening, there is no play of light reflected on the lower layers of the atmosphere, this twilight seems unusual and strange. The landscape seems to blur into something; the grass loses its greenness, the mountains seem to lose their heavy density.

However, while the thin crescent-shaped rim of the sun remains, the impression of a very pale day still reigns, and it seemed to me that the stories of darkness during the eclipse were exaggerated. “Is it really possible,” I thought, “that this remaining insignificant spark of the sun, burning like the last forgotten candle in the vast world, means so much?.. Is it really possible that when it goes out, night should suddenly fall?”

But that spark disappeared. Somehow, impetuously, as if breaking out with an effort from behind a dark curtain, it sparkled with another golden splash and went out. And with this, thick darkness poured onto the earth. I caught the moment when a complete shadow appeared in the darkness. It appeared in the south and, like a huge blanket, quickly flew over the mountains, along rivers, across fields, fanning the entire heavenly space, wrapped us up and in an instant closed in the north. I now stood below, on the shore shallows, and looked back at the crowd. Deathly silence reigned in it... The figures of people merged into one dark mass...

But this was no ordinary night. It was so light that the eye involuntarily looked for the silvery moonlight, piercing through the blue darkness of an ordinary night. But there was no shine anywhere, no blue. It seemed as if thin ash, indistinguishable to the eye, was scattered from above the ground, or as if the thinnest and thickest mesh hung in the air. And there, somewhere on the sides, in the upper layers, one feels an illuminated airy distance that shines through into our darkness, merging the shadows, depriving the darkness of its shape and density. And over all the confused nature of a wonderful panorama, clouds run, and among them a breathtaking struggle takes place... A round, dark, hostile body, like a spider, glared at the bright sun, and they rush together in the sky-high heights. A kind of radiance, flowing in changeable tints from behind the dark shield, gives the spectacle movement and life, and the clouds further enhance the illusion with their alarming, silent running.”

Lunar eclipses do not represent for modern astronomers the exceptional interest that is associated with solar eclipses. Our ancestors saw lunar eclipses as convenient opportunities to confirm the spherical shape of the Earth. It is instructive to recall the role this evidence played in the history of Magellan’s circumnavigation of the world. When, after a tiring long journey through the deserted waters of the Pacific Ocean, the sailors fell into despair, deciding that they had irrevocably moved away from solid land into an expanse of water that would never end, Magellan alone did not lose courage. “Although the church constantly insisted on the basis of the Holy Scriptures that the Earth is a vast plain surrounded by waters,” says the companion of the great navigator, “Magellan drew firmness from the following consideration: during eclipses of the Moon, the shadow cast by the Earth is round, and what is the shadow, so must there may also be an object throwing it...” In ancient books on astronomy we even find drawings explaining the dependence of the shape of the lunar shadow on the shape of the Earth (Fig. 57).

Rice. 57. An ancient drawing explaining the idea that by the appearance of the earth’s shadow on the disk of the Moon one can judge the shape of the Earth

Now we no longer need such evidence. But lunar eclipses make it possible to judge the structure of the upper layers terrestrial atmosphere based on the brightness and color of the Moon. As you know, the Moon does not disappear without a trace in the earth’s shadow, but continues to be visible in the sun’s rays, bending inside the shadow cone. The strength of the Moon's illumination at these moments and its color shades are of great interest for astronomy and are, as has been established, in an unexpected relationship with the number of sunspots. In addition, the phenomena of lunar eclipses have recently been used to measure the rate of cooling of the lunar soil when it is deprived of solar heat (we will return to this later).

Why do eclipses repeat after 18 years?

Long before our era, Babylonian sky observers noticed that a series of eclipses - both solar and lunar - were repeated every 18 years and 10 days. This period was called “Saros”. Using it, the ancients predicted the onset of eclipses, but they did not know what determined such a regular periodicity and why “saros” has exactly this and not another duration. The rationale for the periodicity of eclipses was found much later, as a result of a careful study of the movement of the Moon.

What is the Moon's orbital time? The answer to this question may vary depending on the moment at which the Moon’s revolution around the Earth is considered complete. Astronomers distinguish five kinds of months, of which only two are of interest to us now:

1. The so-called “synodic” month, i.e. the period of time during which the Moon makes a full revolution in its orbit, if you monitor this movement from the Sun. This is the period of time that passes between two identical phases of the Moon, for example, from new moon to new moon. It is equal to 29.5306 days.

2. The so-called draconic month, i.e. the period after which the Moon returns to the same “node” of its orbit ( node – intersection of the lunar orbit with the plane of the earth’s orbit). The duration of such a month is 27.2122 days.

Eclipses, as is easy to understand, occur only at moments when the Moon, in the full moon or new moon phase, is at one of its nodes: then its center is on the same straight line with the centers of the Earth and the Sun. Obviously, if an eclipse occurs today, then it must occur again after such a period of time that integer number of synodic and draconic months : then the conditions under which eclipses occur will be repeated.

How to find similar time periods? To do this we need to solve the equation

Where X And y – whole numbers. Presenting it as a proportion

we see that the smallest accurate the solutions to this equation are:

x = 272 122………. y = 295,306.

It turns out to be a huge, tens of thousands of years, period of time, practically useless. Ancient astronomers were content with the solution close . The most convenient means for finding approximations in such cases is provided by continued fractions. Let's expand the fraction

to continuous. It works like this. Eliminating the integer, we have

In the last fraction, divide the numerator and denominator by the numerator:

Numerator and denominator of fraction

divide by the numerator and do the same in the future. We end up getting

From this fraction, taking its first links and discarding the rest, we obtain the following successive approximations:

The fifth fraction in this series already gives sufficient accuracy. If you dwell on it, i.e. accept x = 223, a y = 242, then the recurrence period of eclipses will be equal to 223 synodic months, or 242 draconic.

This amounts to 6585 1/3 days, i.e. 18 years 11.3 days (or 10.3 days).

This is the origin of saros. Knowing where it came from, we can understand how accurately eclipses can be predicted with its help. We see that, considering saros equal to 18 years 10 days, 0.3 days are discarded. This should mean that eclipses planned for such a shortened period will occur at other watches day than the previous time (about 8 hours later), and only when using a period equal to triple exact Saros, eclipses will be repeated at almost the same moments of the day. In addition, Saros does not take into account changes in the distance of the Moon from the Earth and the Earth from the Sun, changes that have their own periodicity; These distances determine whether the solar eclipse will be total or not. Therefore, Saros makes it possible to predict only that an eclipse will occur on a certain day, but whether it will be total, partial or annular, and whether it can be observed in the same places as the previous time, cannot be stated.

Finally, it also happens that an insignificant partial eclipse of the Sun after 18 years reduces its phase to zero, that is, it is not observed at all; and, conversely, sometimes small partial eclipses of the Sun that have not been observed before become visible.

Astronomers don't use saros these days. The capricious movements of the earth's satellite have been studied so well that eclipses are now predicted to the nearest second. If the predicted eclipse had not occurred, modern scientists would be ready to admit anything but the error of the calculations. This was aptly noted by Jules Verne, who in his novel “Land of Furs” talks about an astronomer who went on a polar journey to observe a solar eclipse. Contrary to the prediction, it did not happen. What conclusion did the astronomer draw from this? He announced to those around him that the ice field on which they were located was not a continent, but a floating ice floe carried by the sea current beyond the eclipse band. This statement was soon justified. Here is an example of deep faith in the power of science!

Is it possible to?

Eyewitnesses say that during a lunar eclipse they happened to observe the disk of the Sun on one side of the sky near the horizon and at the same time on the other side the darkened disk of the Moon.

Similar phenomena were observed in 1936 - on the day of a partial lunar eclipse on July 4. “4th of July in the evening at 8 p.m. 31 min. The moon rose, and at 20 o'clock. 46 min. The Sun was setting, and at the moment the Moon was rising, a lunar eclipse occurred, although the Moon and the Sun were visible simultaneously above the horizon. I was very surprised by this, because light rays travel in a straight line,” one of the readers of this book wrote to me.

The picture is truly mysterious: although, contrary to the belief of Chekhov’s girl, it is impossible to “see the line connecting the center of the Sun and the Moon” through smoked glass, but mentally drawing it past the Earth with such an arrangement is quite possible. Can an eclipse occur if the Earth does not block the Moon from the Sun? Can such an eyewitness account be trusted?

In reality, however, there is nothing incredible in such an observation. The fact that the Sun and the darkened Moon are visible in the sky at the same time is due to the bending of light rays in the Earth's atmosphere. Thanks to this curvature, called “atmospheric refraction,” each luminary appears to us higher its true position (p. 48, fig. 15). When we see the Sun or Moon near the horizon, they are geometrically located below horizon. It is therefore not impossible that the disk of the Sun and the darkened Moon are both visible above the horizon at the same time.

“Usually,” Flammarion says in this regard, “they point to the eclipses of 1666, 1668 and 1750, when this strange feature manifested itself most sharply. However, there is no need to go that far. February 15, 1877 The moon rose in Paris at 5 o'clock. 29 min. The sun set at 5 o'clock. 39 minutes, and, meanwhile, the total eclipse has already begun. On December 4, 1880, a total lunar eclipse occurred in Paris: on this day the Moon rose at 4 o'clock and the Sun set at 4 o'clock 2 minutes, and this was almost in the middle of the eclipse, which lasted from 3 o'clock. 3 min. until 4 o'clock 33 min. If this is not observed much more often, it is only due to a lack of observers. To see the Moon in a total eclipse before sunset or after sunrise, you just need to choose a place on Earth so that the Moon is on the horizon near the middle of the eclipse.”

What not everyone knows about eclipses

1. How long can solar and lunar eclipses last?

2. How many eclipses can occur in one year?

3. Are there years without solar eclipses? And without lunar ones?

4. When will the next total solar eclipse visible in Russia be?

5. During an eclipse, which side does the black disk of the Moon approach the Sun from - right or left?

6. On which edge does the lunar eclipse begin - on the right or on the left?

7. Why do spots of light in the shadow of foliage have the shape of sickles during a solar eclipse (Fig. 58)?

8. What is the difference between the shape of the solar crescent during an eclipse and the shape of a regular crescent of the moon?

9. Why is a solar eclipse viewed through smoked glass?

1. Longest duration full phase solar eclipse 7 3/4 m (at the equator; at higher latitudes - less). Still, the eclipse phases can take up to 3? hours (at the equator).

Duration of all phases lunar eclipse – up to 4 hours; the time of complete darkening of the Moon lasts no more than 1 hour 50 minutes.

2. The number of all eclipses during the year - both solar and lunar - cannot be more than 7 and less than 2. (In 1935, there were 7 eclipses: 5 solar and 2 lunar.)

Rice. 58. Spots of light in the shadow of tree foliage during the partial phase of an eclipse have a crescent shape

3. Without solar Not a single year passes by eclipses: at least 2 solar eclipses occur annually. Years without lunar Eclipses occur quite often, approximately every 5 years.

4. The nearest total solar eclipse visible in Russia will occur on August 1, 2008. The streak of total eclipse will pass through Greenland, the Arctic, Eastern Siberia, and China.

5. In the northern hemisphere of the Earth, the disk of the Moon approaches the Sun from right to left. The first contact of the Moon with the Sun should always be expected with right sides. In the southern hemisphere - from left (Fig. 59).

Rice. 59. Why does an observer in the northern hemisphere of the Earth see the disk of the Moon approaching the Sun during an eclipse? on right, and for an observer in the southern hemisphere – left?

6. In the northern hemisphere, the Moon enters the earth's shadow with its left edge, in the south - right.

7. Spots of light in the shadow of foliage are nothing more than images of the Sun. During an eclipse, the Sun has the shape of a sickle and its images in the shadow of foliage should have the same appearance (Fig. 58).

8. Lunar the sickle is limited on the outside by a semicircle, on the inside by a semi-ellipse. Solar the sickle is limited by two arcs of a circle of the same radius (see page 59, “Riddles of the lunar phases”).

9. You cannot look at the Sun, even if partially obscured by the Moon, with unprotected eyes. The sun's rays burn the most sensitive part of the retina of the eye, significantly reducing visual acuity for a long time, and sometimes for life.

Back at the beginning of the 13th century. The Novgorod chronicler noted: “From this same sign in Veliky Novgorod, hardly anyone lost sight of a person.” However, it is easy to avoid burns if you stock up on heavily smoked glass. You need to smoke it on a candle so thickly that the disk of the Sun appears through such glass sharply outlined circle , without rays and halo; for convenience, the smoked side is covered with another, clean glass and pasted around the edges with paper. Since it is impossible to foresee in advance what the visibility conditions of the Sun will be during the hours of an eclipse, it is useful to prepare several glasses with different darkness densities.

You can also use colored glass if you put together two glasses of different colors (preferably “complementary”). Ordinary canned dark glasses are not sufficient for this purpose.

What's the weather like on the Moon?

Strictly speaking, there is no weather on the Moon, if this word is understood in the usual sense. What kind of weather can there be where there is absolutely no atmosphere, clouds, water vapor, precipitation, or wind? The only thing we can talk about is soil temperature.

So how hot is the Moon's soil? Astronomers now have an instrument that makes it possible to measure the temperature of not only distant bodies, but also their individual parts. The design of the device is based on the phenomenon of thermoelectricity: an electric current runs in a conductor soldered from two dissimilar metals when one junction is warmer than the other; the strength of the resulting current depends on the temperature difference and allows you to measure the amount of absorbed heat.

The sensitivity of the device is amazing. With microscopic dimensions (the critical part of the device is no more than 0.2 mm and weighs 0.1 mg), it responds even to the heating effect of 13th magnitude stars, which increases the temperature ten millionths of a degree . These stars are not visible without a telescope; they shine 600 times weaker than stars located at the limit of visibility with the naked eye. Capturing such a tiny amount of heat is like detecting the warmth of a candle from a distance of several kilometers.

Having such an almost miraculous measuring device, astronomers inserted it into separate areas of the telescopic image of the Moon, measured the heat it received and, on this basis, estimated the temperature of various parts of the Moon (with an accuracy of 10°). Here are the results (Fig. 60): in the center of the disk of the full Moon the temperature is above 100°; Water poured here onto the lunar soil would boil even under normal pressure. “On the Moon we wouldn’t have to cook our lunch on a stove,” writes one astronomer, “any nearby rock could fill its role.” Starting from the center of the disk, the temperature decreases evenly in all directions, but another 2700 km from the central point it is not lower than 80°. Then the temperature drops faster, and near the edge of the illuminated disk a frost of -50° prevails. It is even colder on the dark side of the Moon, facing away from the Sun, where frost reaches -170°.

Rice. 60. The temperature on the Moon reaches +125 °C in the center of the visible disk during the full moon and quickly drops towards the edges to -50 ° and below

It was mentioned earlier that during eclipses, when the lunar globe is plunged into the earth's shadow, the soil of the Moon, deprived of sunlight, quickly cools. It was measured how great this cooling was: in one case, a drop in temperature during an eclipse was found from +125 to -115 °, i.e., almost 240 ° within some I 1/-2 hours. Meanwhile, on Earth, under similar conditions, i.e. during a solar eclipse, there is a decrease in temperature by only two, or even three degrees. This difference must be attributed to the earth’s atmosphere, which is relatively transparent to the visible rays of the Sun and blocks the invisible “heat” rays of the heated soil.

The fact that the soil of the Moon so quickly loses the heat it has accumulated indicates both the low heat capacity and the poor thermal conductivity of the lunar soil, as a result of which, when it is heated, only a small reserve of heat has time to accumulate.