Why does the shape of the moon change? Why does the moon change throughout the month

The sun has just set. Against the background of a reddish dawn, a narrow, shiny sickle looms brightly, with a hump facing the setting Sun. It doesn't take long to admire them. Soon it will follow the Sun below the horizon. At the same time they say: "A new moon was born."

Photo: V.Ladinsky. A new moon is born.

The next day at sunset, you will notice that the crescent has become wider, it is visible higher above the horizon and sets not so early. Every day the Moon seems to grow and at the same time moves away from the Sun farther and farther to the left (to the east). A week later, the Moon is in the evening in the south in the form of a semicircle with a bulge to the right. Then they say: "The moon has reached the phase first quarter».

The best time of the year to observe the young Moon in the Northern Hemisphere of the Earth is spring, when the crescent of the new moon rises high above the horizon. In the phase of the first quarter, the Moon rises highest above the horizon for us at the end of winter - the beginning of spring.

In the following days, the Moon continues to grow, becomes more of a semicircle and moves even further to the east, until a week later it becomes a full circle, i.e. will come full moon. At the time when the Sun will go under the western horizon for west side, from the opposite, eastern side, the full moon will begin to rise. By morning, both luminaries seem to change places: the appearance of the Sun in the east finds the full Moon setting in the west.

The full moon is highest above the horizon in the first half of winter, and on short summer nights it can be found low in the southern sky around midnight.

Photo: V.Ladinsky. Full moon rising July 21, 2005.

Then day after day the moon rises later and later. It becomes more and more truncated, or damaged, but on the right side. A week after the full moon, you will not find the moon in the sky in the evening. It is only around midnight that it appears in the east from behind the horizon and again in the form of a half circle, but now directed to the left with a hump. it last(or, as it is sometimes called, the third) quarter. In the morning, the semicircle of the Moon, turned by a hump towards the rising Sun, can be seen in the southern side of the sky. A few days later, the narrow crescent of the Moon, just before sunrise, appears from behind the horizon in the east. And a week later, after the last quarter, the Moon completely ceases to be visible - it comes new moon; then it will appear again on the left side of the Sun: in the evening in the west and again with a hump to the right.

Most favorable time The year for observing the Moon in phases between the last quarter and the new moon is early autumn.

This is how the appearance of the Moon in the sky changes every four weeks, more precisely - 29.5 days. it lunar, or synodic, month. It served as the basis for compiling the calendar in ancient times. Such moon calendar kept by some Eastern peoples and up to the present.

Change lunar phases can be summarized in the following table:

During the new moon, the Moon is between the Earth and the Sun and faces the Earth with its unlit side. In the first quarter, i.e. after a quarter of the moon's revolution, half of its illuminated side is facing the Earth. During the full moon, the Moon is in the opposite side of the Sun, and the entire illuminated side of the Moon is facing the Earth, and we see it in a full circle. In the last quarter, we again see from the Earth half of the illuminated side of the Moon. Now it is clear why the convex side of the crescent of the Moon always faces the Sun.

Within a few days after (or before) the new moon, one can observe, in addition to the bright crescent, the part of the Moon that is not illuminated by the Sun, but is faintly visible. Such a phenomenon is called ashen light. This is the night surface of the Moon, illuminated only by the sun's rays reflected from the Earth.

Thus, the change in the phases of the moon is explained by the fact that the moon revolves around the earth. The time it takes for the moon to revolve around our planet is called sidereal (sidereal) month and is 27.3 days, which is less than 29.5 days, during which the phases of the moon change. The reason for this phenomenon is the movement of the Earth itself. As it revolves around the Sun, the Earth drags along its satellite, the Moon.

On the new moon, when the Moon is between the Earth and the Sun, it can close it from us, then solar eclipse. On a full moon, the Moon, being on the other side of the Earth, can fall into the shadow cast by our planet, then a lunar eclipse will occur. Eclipses do not occur every month because the Moon revolves around the Earth in a plane that does not coincide with the plane (the plane of the ecliptic) in which the Earth revolves around the Sun. The plane of the Moon's orbit is inclined to the plane of the ecliptic at an angle of 5 ° 9 ". Therefore, eclipses occur only when the Moon is near the ecliptic at the time of the new moon (full moon), otherwise its shadow falls "above" or "below" the Earth (or the earth's shadow " above or below the Moon).

Phase is the ratio of the area of ​​the illuminated part of the disk of a celestial body to the area of ​​the entire disk. In the phase of the new moon Ф = 0.0, in the phase of the first and last quarters = 0.5, in the phase of the full moon = 1.0.

A mental line drawn through the tops of the horns of the sickle of the Moon is called the line of horns. It is often said that the line of horns indicates the point of the south, or below it. Perpendicular to the line of horns indicates the direction to the Sun.

If the horns of the lunar month are directed to the left, then the moon is growing, if to the right, then it is aging. However, this rule is reversed when observing the Moon from the southern hemisphere of the Earth, as shown in the figure:

Tasks and questions:

1. The moon is in a new moon. In what phase will the Earth be visible from the Moon? The earth will be in the “full earth” phase, as the phases of the Moon during observations from the Earth and the phases of the Earth for a lunar observer change vice versa and are in antiphase.

2. Is the Earth visible from the Moon in the New Earth? Yes, it is visible in the form of a sickle due to the fact that the Earth's atmosphere refracts sunlight.

3. On December 25 of such and such a year, the Moon was in the phase of the first quarter. In what phase will it be visible in a year? To solve this problem, we take the synodic month of the Moon, which is approximately 29.5 days. Multiply 29.5 by 12 months and get 354 days. Subtract the resulting value from 365 (the number of days in a year) and get 11 days. Given that the first quarter comes after 7 - 8 days, then by adding the obtained value (11) to 7 (or 8), we get the age of the moon in a year, equal to 18 or 19 days. Thus, a year later, the Moon will be in a phase between the full moon and the last quarter.

4. What time will the moon culminate in the first quarter? The moon in the first quarter will culminate over the south point at about six o'clock in the evening local time.

Phases of the Moon in 2012

The movement of the Moon around the planet Earth in orbit takes about a month. In addition, it also moves around its own axis. This process takes a little over 27 days. Since the movement in orbit and rotation around its axis is performed simultaneously, the Moon is always directed towards the Earth by one side.

The moon itself does not shine like the sun. It only gives the impression that it shines, but in fact it only reflects sunlight. As the Moon moves around the planet, sunlight hits different parts of it. This is the answer to the question: "Why is the Moon different?". Periodically, we see the fully illuminated surface of the satellite, and from time to time only part of it is illuminated. Therefore, it seems to us that the moon is changing its shape. But this is only a transformation of the luminary - phases that indicate that we can see its various parts.

Lunar phases, or why the moon is different

The first lunar phase is the new moon. At its moment, the luminary is between the Sun and the Earth. This moon is not visible to us. Then comes the phase in which its side is illuminated by sunlight. This part of it looks like a thin piece of a circle.

Very soon, the side of the Moon that the Sun hits grows and becomes a semicircle. And this lasts until the moon reaches the last quarter, then the cycle ends and starts all over again.

Earth and Moon

The movement of the Earth around its axis coincides with the periods of rotation of the Moon, or is it just the gravitational effect of one celestial body on another? Answer to this question sought by many inquisitive minds.

It has been established that, nevertheless, gravity becomes the cause of this position of celestial bodies. We all know what the tides are, which regularly occur in the oceans and raise the water by several meters.

And the question "why the Moon is different" has a simple answer: the Earth from different sides is subjected to lunar attraction in different ways. The side that is turned towards the satellite is more affected than the opposite.

As a result, various parts of the Earth move in the direction of the side with different speed. The surface, which is directed towards the Moon, swells, in the center the Earth shifts less, and the opposite surface completely lags behind, forming a hump. The Earth's crust is reluctant to change shape, and on land, tidal forces are imperceptible. In the sea, under the influence of the satellite, tidal humps are formed on different sides of the planet.

As it turns to the Moon with its different sides, as a result, the tidal hump also moves along its surface. That's why the moon is different.

Scientists have calculated that a billion years ago, the Moon was located significantly. At this time, there were only 20 hours in a day. Only a few days were required for the Moon to pass around the Earth, and therefore were expressed more clearly. Over time, the motion of the satellite slows down, and in five billion years the Earth will rotate so slowly that it will turn to the Moon with only one side, and there will be only 9 days a year, not 365. It will make nine revolutions per year. Consequently, the year will not have 12 months, as it is now, but only 9, and each will have only one day.

Most people rarely think about how everything works in our world, in what surrounds us. Such things as the change of day and night, the illumination of the planet by the Sun in the daytime, and the Moon at night, have long become our daily routine.

And we don’t often think about how it all “works”. And we all probably noticed that the Moon is systematically changing, taking on a different appearance. And today we will understand why the moon changes during the month.

Does the moon change?

First you need to understand the issue of changing the appearance of our natural satellite. More precisely, it should be noted that, of course, the Moon does not change its appearance. The satellite, as it was, and remains invariably a solid, spherical and lifeless body.

In addition, it should be noted that the expression about the change of the moon during the month is not entirely correct. The fact is that the satellite changes its appearance, or rather, we see it in different form within 8 days, and these 8 phases are cyclically repeated all the time, that is, within one month such a change occurs almost four times.

And now let's figure out why the appearance of the moon changes during the month.

The very process of changing appearance, in which our satellite appears before the Earth at night, has long received its scientific name: “Phases of the Moon”. And there are only 8 such phases, among which the initial one was called “New Moon”, and the final, eighth in a row, “Old Moon”.

In order to understand what is the nature of the change in the picture that we have the opportunity to observe in the clear night sky, we need to remember why the Moon glows. And the nature of the glow of our satellite is extremely simple: it has a specific surface that reflects the rays of the Sun from itself and redirects them to the surface of the Earth.

However, as you know, the satellite makes movements around our planet, therefore, it is always illuminated by the Sun in different ways: sometimes the Earth obscures the sun's rays from it completely, and sometimes - partially. At the same time, sometimes the sun illuminates and reverse side The moon, inaccessible to the human eye. That is why there are such phases of the Moon, during which people from the surface of the Earth have the opportunity to observe only that part of the satellite that is illuminated by the rays of the Sun. This is why the moon changes throughout the month.

As you know, the moon does not emit light, but only reflects it. And therefore in the sky only that side of it, which is illuminated by the Sun, is always visible. This side is called the day side. Moving across the sky from west to east, the Moon overtakes and overtakes the Sun during the month. There is a change in the relative position of the Moon, Earth and Sun. In this case, the sun's rays change the angle of incidence on the lunar surface and therefore the part of the Moon visible from the Earth changes. The movement of the moon across the sky is usually divided into phases that are directly related to its modification: new moon, young moon, first quarter, full moon and last quarter.

Moon observations

The moon is a spherical celestial body. That is why, when it is partially illuminated by sunlight from the side, the appearance of a “sickle” appears. By the way, by the illuminated side of the Moon, you can always determine which side the Sun is on, even if it is hidden behind the horizon.

The duration of the complete change of all lunar phases is usually called the synodic month and it ranges from 29.25 to 29.83 Earth solar days. The duration of the synodic month varies due to the elliptical shape of the lunar orbit.

On the new moon, the disk of the Moon is absolutely invisible in the night sky, since at that time it is located as close as possible to the Sun and at the same time faces the Earth at night.

Next comes the new moon phase. During this period of time, for the first time in a synodic month, the Moon becomes visible in the night sky in the form of a narrow crescent and can be observed at dusk a few minutes before it sets.

Next comes the first quarter. This is the phase in which exactly half of its visible part is illuminated, as in the last quarter. The only difference is that in the first quarter, the proportion of the illuminated part at this moment increases.

The full moon is the phase in which the lunar disk is visible clearly and completely. During the full moon for several hours, you can observe the so-called opposition effect, in which the brightness of the lunar disk noticeably increases, while its size remains the same. This phenomenon is explained quite simply: for an earthly observer, at this moment all shadows on the surface of the Moon disappear.

There are also phases of the growing, waning and old moon. All of them are characterized by a very narrow crescent of the Moon, a greyish-ashy color typical of these phases.

From all of the above, we can conclude that, in fact, nothing obscures the Moon. It just changes the angle of its illumination by the sun's rays.

Brief information The Moon is the Earth's natural satellite and the brightest object in the night sky. The force of gravity on the Moon is 6 times less than on Earth. The difference between day and night temperatures is 300°C. The rotation of the moon around its axis occurs with a constant angular velocity in the same direction in which it revolves around the Earth, and with the same period of 27.3 days. That is why we see only one hemisphere of the Moon, and the other, called the far side of the Moon, is always hidden from our eyes.


Moon phases. The numbers are the age of the moon in days. Details on the moon depending on the equipment Due to its proximity, the Moon is a favorite object for astronomy lovers, and deservedly so. Even the naked eye is enough to get a lot of pleasant impressions from contemplating our natural satellite. For example, the so-called "ash light" that you see when observing the thin crescent of the Moon is best seen in the early evening (at dusk) on a waxing or early morning on a waning Moon. Also, without an optical instrument, interesting observations can be made of the general outlines of the Moon - seas and land, the ray system surrounding the Copernicus crater, etc. By pointing binoculars or a small low-power telescope at the Moon, you can study the lunar seas, the largest craters and mountain ranges in more detail. Such an optical device, not too powerful at first glance, will allow you to get acquainted with all the most interesting sights of our neighbor. As the aperture grows, the number of visible details also increases, which means that there is an additional interest in studying the Moon. Telescopes with a lens diameter of 200 - 300 mm make it possible to examine fine details in the structure of large craters, to see the structure of mountain ranges, to examine many furrows and folds, and to see unique chains of small lunar craters. Table 1. Capabilities of various telescopes

The Moon is a very bright object that, when viewed through a telescope, often simply dazzles the observer. To reduce brightness and make observations more comfortable, many amateur astronomers use an ND filter or a variable density polarizing filter. The latter is more preferable, as it allows you to change the level of light transmission from 1 to 40% (Orion filter). Why is it convenient? The fact is that the amount of light coming from the moon depends on its phase and the magnification applied. Therefore, when using a conventional ND filter, you will occasionally encounter a situation where the image of the moon is either too bright or too dark. The variable density filter is free from these disadvantages and allows you to set a comfortable brightness level if necessary.

Orion Variable Density Filter. Demonstration of the possibility of selecting the filter density depending on the phase of the moon

When is the best time to see the moon?
At first glance it seems absurd, but the full moon is not the most best time to observe the moon. The contrast of lunar features is minimal, making it almost impossible to observe them. During the "lunar month" (the period from new moon to new moon), there are two most favorable periods for observing the moon. The first begins shortly after the new moon and ends two days after the first quarter. This period is preferred by many observers, since the visibility of the Moon falls on the evening hours.

Second favorable period begins two days before the last quarter and lasts almost until the new moon. These days, the shadows on the surface of our neighbor are especially long, which is clearly visible on the mountainous terrain. Another plus of observing the Moon in the phase of the last quarter is that in the morning the atmosphere is calmer and cleaner. Due to this, the image is more stable and clear, which makes it possible to observe finer details on its surface.

Another important point is the height of the moon above the horizon. The higher the Moon, the less dense layer of air overcomes the light coming from it. Therefore, there is less distortion, and better quality Images. However, the height of the moon above the horizon varies from season to season.

When planning your observations, be sure to open your favorite planetarium program and determine the hours of the best visibility.
The moon moves around the earth in an elliptical orbit. The average distance between the centers of the Earth and the Moon is 384,402 km, but the actual distance varies from 356,410 to 406,720 km, due to which the apparent size of the Moon varies from 33" 30"" (at perigee) to 29" 22"" (apogee). ).

Of course, you should not wait until the distance between the Moon and the Earth is minimal, just note that at perigee one can attempt to consider those details of the lunar surface that are at the limit of visibility.

Starting observations, point your telescope to any point near the line that divides the moon into two parts - light and dark. This line is called the terminator, being the boundary of day and night. During the growing moon, the terminator indicates the place of sunrise, and during the waning - sunset.

When observing the Moon in the terminator region, you can see the tops of the mountains, which are already illuminated by the sun's rays, while the lower part of the surface surrounding them is still in shadow. The scenery along the terminator line changes in real time, so if you spend a few hours at the telescope observing this or that lunar landmark, your patience will be rewarded with an absolutely stunning sight.

What to see on the moon

craters- the most common formations on the lunar surface. They got their name from Greek word denoting "cup". Most of the lunar craters are of impact origin, i.e. formed as a result of the impact of a cosmic body on the surface of our satellite.

Moon Seas- dark areas that stand out clearly on the lunar surface. At its core, the seas are lowlands that occupy 40% of the entire surface area visible from the Earth.

Look at the moon on a full moon. The dark spots that form the so-called "face on the moon" are nothing more than lunar seas.

Furrows- lunar valleys, reaching a length of hundreds of kilometers. Quite often, the width of the furrows reaches 3.5 km, and the depth is 0.5–1 km.

Folded veins- on appearance resemble ropes and appear to be the result of deformation and compression caused by the sinking of the seas.

mountain ranges- lunar mountains, the height of which ranges from several hundred to several thousand meters.

Domes- one of the most mysterious formations, since their true nature is still unknown. On the this moment only a few dozen domes are known, which are small (as a rule, 15 km in diameter) and low (several hundred meters), round and smooth elevations.

How to observe the moon
As mentioned above, observations of the Moon should be carried out along the terminator line. It is here that the contrast of lunar details is maximum, and thanks to the play of shadows, unique landscapes of the lunar surface open up.

When looking at the Moon, experiment with magnification and find the most appropriate for the given conditions and for this object.
In most cases, three eyepieces will suffice for you:

1) An eyepiece that gives a small increase, or the so-called search one, which allows you to comfortably view the full disk of the moon. This eyepiece can be used for general sightseeing, lunar eclipse viewing, and lunar excursions for family and friends.

2) An eyepiece of medium power (about 80-150x, depending on the telescope) is used for most observations. It will also be useful in unstable atmospheres where high magnification is not possible.

3) A powerful eyepiece (2D-3D, where D is the diameter of the lens in mm) is used to study the lunar surface in detail at the limit of the telescope's capabilities. Requires good atmospheric conditions and complete thermal stabilization of the telescope.

Your observations will become more productive if they are focused. For example, you can start your study with the list " ", compiled by Charles Wood. Also pay attention to the series of articles "" that talk about lunar sights.

Another fun activity can be looking for tiny craters visible at the limit of your equipment.

Make it a habit to keep an observation diary in which you regularly record the conditions of observation, the time, the phase of the moon, the state of the atmosphere, the magnification used, and a description of the objects you see. Such records can be accompanied by sketches.

10 most interesting lunar objects

(Sinus Iridum) T (moon age in days) - 9, 23, 24, 25
It is located in the northwestern part of the moon. Viewable with 10x binoculars. In a telescope at medium magnification is an unforgettable sight. This ancient 260 km diameter crater has no rim. Numerous small craters dot the remarkably flat bottom of Rainbow Bay.










(Copernicus) T - 9, 21, 22
One of the most famous lunar formations is visible with a small telescope. The complex includes the so-called system of rays, extending for 800 km from the crater. The crater is 93 km in diameter and 3.75 km deep, making sunrises and sunsets over the crater a breathtaking sight.









(Rupes Recta) T - 8, 21, 22
A tectonic fault 120 km long, easily visible in a 60 mm telescope. A straight wall runs along the bottom of a ruined ancient crater, traces of which can be found on the east side of the fault.











(Rümker Hills) T - 12, 26, 27, 28
A large volcanic dome visible with a 60mm telescope or large astronomical binoculars. The hill has a diameter of 70 km and maximum height 1.1 km.











(Apennines) T - 7, 21, 22
The mountain range is 604 km long. Easily visible with binoculars, but its detailed study requires a telescope. Some peaks of the ridge rise above the surrounding surface for 5 or more kilometers. In some places mountain range cross furrows.










(Plato) T - 8, 21, 22
Visible even with binoculars, the Plato crater is a favorite among astronomers. Its diameter is 104 km. The Polish astronomer Jan Hevelius (1611-1687) named this crater "Great Black Lake". Indeed, through binoculars or a small telescope, Plato looks like a large dark spot on the bright surface of the moon.









Messier and Messier A (Messier and Messier A) T - 4, 15, 16, 17
Two small craters that require a telescope with a 100 mm objective lens to observe. Messier has an oblong shape measuring 9 by 11 km. Messier A is slightly larger - 11 by 13 km. To the west of the craters Messier and Messier A, two bright beams 60 km long stretch.










(Petavius) T - 2, 15, 16, 17
Despite the fact that the crater is visible in small binoculars, a truly breathtaking picture opens up in a telescope with a high magnification. The domed bottom of the crater is dotted with furrows and cracks.











(Tycho) T - 9, 21, 22
One of the most famous lunar formations, famous mainly due to the giant system of rays surrounding the crater and extending for 1450 km. The rays are perfectly visible through small binoculars.











(Gassendi) T - 10, 23, 24, 25
The oval crater, elongated for 110 km, is accessible for observation with 10x binoculars. The telescope clearly shows that the bottom of the crater is dotted with numerous crevices, hills, and there are also several central hills. A careful observer will notice that the walls near the crater have been destroyed in some places. At the northern end is the small crater Gassendi A, which, together with its older brother, resembles a diamond ring.