Why does the moon vary throughout the month? Why does the Moon change shape? Moon phases Why do we see a month

Some people answer this question without thinking: the Moon is covered by the Earth’s shadow. This is the wrong answer, because the Earth's shadow is always directed in the direction opposite to the Sun, and Moon, moving along its orbit, circles the Earth on all sides.

“Astronomers carefully study the movement of the Moon and describe it formula, containing in general about 700 components, and calculations are carried out with an accuracy of 15 decimal places"(I.A. Klimishin “Astronomy of our days”, M. “Science”, third edition, p. 95).

Such precision is necessary for astronautics.

In this article, without delving into details, we will consider only the simplest question: why the appearance of the Moon changes, or, in other words, why the lunar phases and conditions of their visibility change.

The figure shows that wherever the Moon is in orbit, half of it is illuminated by the Sun, here it is day on the Moon, and the other half is dark, night. An observer on Earth can only see the side of the Moon that faces Earth. From it, only the part illuminated by the Sun is visible. The outer circle of the figure shows what the Moon looks like from the point of view of an observer standing on Earth. In position (1), most of the night side of the Moon and a small part of the day side are facing the earthly observer; it is this side that looks like a narrow crescent. With each passing day, the Moon advances in its orbit, as indicated by the arrow, and the corresponding observer on Earth is able to see an increasing proportion of the day side of the Moon. In positions (2) and (3) it is clear that the Moon is gradually “growing”.

In position (4), the Moon is opposite the Sun, and the entire day side of the Moon faces the Earth. This phase is called the full moon. Why did the Moon not fall into the shadow of the Earth, directed in the direction opposite to the Sun? Because the plane of the lunar orbit is inclined to the plane of the Earth's orbit at an angle of 5 degrees 9 minutes, and the Earth's shadow usually passes by the Moon. The moon falls into the earth's shadow only during lunar eclipses, the conditions for the occurrence of which must be specially considered.

After the full moon, the daily fraction of the Moon visible from the Earth gradually decreases - phases (5), (6), (7). The latter is again a narrow crescent, but from the point of view of an observer standing on Earth in position (7), its horns are directed in the direction opposite to the growing crescent and resemble the letter “C”.

Then comes the new moon phase (8). The Moon is above the daytime side of the Earth, faces the Earth at night and is lost in the bright daytime sky. At this time the nights are dark and moonless.

To make it easier to understand when which phases are visible, the drawing is made in such a way that we are looking at the Earth and the Moon’s orbit “from above,” from the Earth’s north pole, which is placed in the center of the drawing. The sun's rays illuminate the daytime half of the Earth. The arrow shows the direction of the Earth's daily rotation and, accordingly, the change of day to evening, night and morning. Approximately 28 Earth days (lunar month) will pass in the time it takes the Moon to make a full revolution around the Earth. The phase change occurs gradually and continuously. Between the described phases, 3-4 days pass.

The duration of the lunar month differs from the duration of the solar month, therefore the same lunar phases occur on different dates of our solar calendar.

Due to the movement of the Moon in its orbit, its rising, culmination and setting occur almost 50 minutes later than in the previous day, so the visibility of the Moon shifts to an increasingly later time.

In position (1), the young crescent rose before dark and before it sets behind the western horizon, it can be seen in the early evening after sunset. In position (2), the Moon rises at sunset and is visible throughout the evening. In position (3), the visibility time is shifted to the first half of the night. In a full moon (4) the moon shines all night. After the full moon, the visibility of the Moon first changes to the second half of the night (5), then to the morning (6) and to twilight before sunrise (7). During a new moon, the Moon is not visible at all.

Sun and Earth on the Moon's sky

The Earth's disk is 15 times larger than the lunar disk, visible from the Earth, in addition, the Earth shines much brighter than our Moon, since it reflects 40% of sunlight (oceans, ice, clouds), and the Moon only 12% (basalts, dusty areas ). As the Moon moves through its orbit, an observer on the Moon sees the changing phases of the Earth, but the boundary between the light and dark regions of the Earth is not clear, but blurred due to clouds and light scattered in the atmosphere. From the Moon you can see clouds floating above the Earth, notice the daily rotation of the Earth, because during the lunar day it makes thirty revolutions around its axis.

Let's see what happens in the sky of the Moon during its day.

In the east, the sky began to brighten, but this is not dawn; the corona of the Sun is slowly rising from the horizon. When the Sun rises in the black sky with a crown, the Earth looks like half: part day and part night. The sun rises very slowly, because the day lasts 15 of our days. While the Sun reaches its highest position, the light part of the Earth decreases, turning into a thin crescent, complemented by a light blurred border to the circumference.

At lunar noon, the Earth faces the Moon on its night side, its dark disk surrounded by an orange-red halo. The fact is that sunlight passes through the Earth’s atmosphere, and the size of the particles of the Earth’s atmosphere is such that they scatter short-wave, blue, light from the solar spectrum, and long-wave, red-orange light passes through the atmosphere freely. This phase can be called new earth by analogy with the new moon. In the afternoon, the Sun slowly descends to the west, and the crescent of the Earth gradually grows and turns into a half by sunset.

Night time is coming. At lunar midnight, the Earth faces the Moon with its day side, the full disk of the Earth illuminates the lunar landscape with bluish-greenish light. This is how the blue Earth's atmosphere and green areas of the Earth change the reflected sunlight.

By the next sunrise, the Earth will again take the form of a half-disk.

RMR_astra writes:

In the black starry sky of the Moon, the Sun rises and sets, and the Earth, swaying slightly, stands in one place.

I'm not kidding. The earth may rise. It all depends on where the observer is on the surface of the Moon. And these sunrises and sunsets are connected with....

Right. With libration (swaying) of the Moon in latitude and longitude.

And the day lasts longer than a day

A lunar day lasts 14 earthly days, and the night lasts the same amount; a lunar day is equal to a lunar month. Why are the days so long? Why does the Moon rotate so slowly on its axis?

It once spun faster, but was slowed down by the Earth. The Earth causes a tidal wave in the Moon's body. The Moon rotated around its axis, and the tidal wave, which is always directed towards the Earth, rolled along the surface of the Moon in the direction opposite to its rotation.

Now the Moon rotates so that the tidal hump does not roll, but always “looks” at the Earth. Therefore, the shape of the Moon slightly resembles an egg, and therefore the Moon always faces the Earth with its more convex side.

Only about half of the Moon is visible from Earth, and Earthlings first saw what the opposite side looked like when the Soviet Luna 3 station transmitted an image of it to Earth.

How little we know even about the Moon. I adhere to the lunar calendar when working in the country and visiting the hairdresser. Resolve the question, dear RMR_astra.

If the Moon is always facing us the same way, why then in the lunar calendar there are 28, 29 or 30 lunar days in different months?

It is convenient to divide your question into two questions: is the side of the Moon facing us really equal to half of its surface, and how accurately does the lunar calendar describe its movement.

We have already noted that the movement of the Moon is very complex, therefore, as before, we will take into account only the main factors. The orbit of the moon is not a circle, but an ellipse, so it becomes possible to look beyond the left side of the lunar disk, then beyond the right, so not 0.5, but 0.6 shares of the lunar surface are accessible from Earth.

The period of the daily rotation of the Moon coincides with its complete revolution around the Earth relative to the stars (27.3 Earth days), and the phases of the Moon are determined by the complete revolution of the Moon around the Earth relative to the Sun. This period is slightly longer, since during one revolution the Moon, together with the Earth, manages to move along the Earth’s orbit (29.5 Earth days). Since these inaccuracies are not noticeable to the naked eye, as a first approximation it is assumed that half of the Moon is visible from the Earth.

The lunar calendar is based on a period of changing phases, contains 12 lunar months, and the length of the year is 355 days, that is, 10 days less than the solar calendar, which corresponds to agricultural seasons. Over time, the lunar and solar calendars diverged so much that, in order to bring them together, some countries added a 13th month to the lunar calendar (not every year), while others preferred to add days to some months. These calendar changes have virtually no effect on the correctness of determining the lunar phases and on the validity of the statement that the Moon faces the Earth with one side.

It should also be noted that the illumination of the earth's surface by the Sun is almost 1,000,000 times greater than by the full Moon.

I am not interested in predictions of either the lunar or astrological calendar, but in connection with your question, I read it on the Internet.

A scientific prediction differs from a pseudoscientific one in that in the first case it answers the questions “Why?”, “How?”, “What is the mechanism of influence?” etc. For example, BY STUDYING the movements of the Moon and the Earth, it is possible to predict when a solar eclipse will occur, in which areas it will be observed, how long it will last, what fraction of the Sun will be covered by the Moon.

In the second case, the listed questions do not even arise for either the authors or the users of their predictions. Because of misunderstanding, they say: “There must be something in this.”

But you are a thinking person, try to understand what the connection is between the Moon and your hair. If you explain it to me, I will be grateful to you.

Good afternoon, dear RMR_astra.

Thanks to you, I understood why a variety of information from the Internet is not absorbed. She is impersonal. And when the ray of knowledge is directed at you personally, it hits the target. Now the difference between the words “about half” and “exactly half” is clear.

Before your question, the lunar calendar was not in doubt at all. I know well gardeners who always adhere to the lunar calendar, and their fruits ripen faster than their neighbors. But this, of course, can be explained by better care and constant care. They even talk to plants and treat them as if they were alive.

The connection between the Moon and hair. If there really is no scientific explanation, then it is the concept of FAITH. Some patients recover after taking a placebo pacifier, so why not believe in the power of the waxing moon?

If we observe the Moon for a month, we will notice that it gradually changes its appearance from a full disk to a narrow crescent and then, after 2–3 days, when it is invisible, in the reverse order - from a crescent to a full disk. Moreover, the shape, or phases, of the Moon changes from month to month strictly periodically. The planets Mercury and Venus also change their appearance, but only over a longer period of time. The phase change occurs due to periodic changes in the lighting conditions of the named celestial bodies in relation to the observer. Illumination depends on the relative position of the Sun, the Earth and each of the bodies in question.

Phases of the Moon and its appearance for an earthly observer.

When the Moon is between the Sun and the Earth on the straight line connecting these two luminaries, in this position the unlit part of the lunar surface faces the Earth, and we do not see it. This phase is the new moon. 1–2 days after the new moon, the Moon moves away from the straight line connecting the centers of the Sun and the Earth, and from the Earth we can see a narrow lunar crescent, convexly facing the Sun.

During a new moon, the part of the Moon that is not illuminated by direct sunlight is still slightly visible against the dark background of the sky. This glow was called the ashen light of the Moon. Leonardo da Vinci was the first to correctly explain the reason for this phenomenon: the ashen light arises due to the sun's rays reflected from the Earth, which at that time is facing the Moon with most of its sunlit hemisphere.

A week after the new moon, the terminator - the boundary between the illuminated by the Sun and the dark part of the lunar disk - takes on the appearance of a straight line for an earthly observer. The illuminated part of the Moon is exactly half of the visible disk; this phase of the moon is called the first quarter. Since at those points of the Moon that are located on the terminator, a lunar day subsequently begins, the terminator during this period of time is called morning.

Two weeks after the new moon, the Moon is again on the line connecting the Sun and the Earth, but this time not between them, but on the other side of the Earth. The full moon occurs when we see the full disk of the Moon illuminated. The two phases of the Moon - new moon and full moon - are collectively called syzygies. During syzygies, eclipses of the Sun and Moon, as well as some other phenomena, can occur. For example, it is during the syzygy period that sea tides reach their greatest magnitude (see Ebbs and flows).

After the full moon, the illuminated part of the Moon begins to decrease, and the evening terminator is visible from the Earth, i.e., the border of the region of the Moon where night falls. Three weeks after the new moon, we again see exactly half of the moon's disk illuminated. The observed phase is the last quarter. The visible crescent of the Moon becomes narrower day by day, and, having gone through a full cycle of changes, the Moon is completely out of sight by the time of the new moon. The full period of phase change - the synodic month - is 29.53 days.

From the new moon to the full moon the Moon is called young or growing, after the full moon it is called old. You can very easily distinguish the crescent of the growing Moon from the waning crescent of the old Moon. If (in the Northern Hemisphere of the Earth) the shape of a sickle resembles the letter C, then the Moon is old. If, by mentally drawing a stick, you can turn the lunar crescent into the letter P, then this is a growing Moon.

The planets Mercury and Venus are also observed in different phases, which are clearly visible through a telescope. People with exceptionally sharp eyesight can observe the phases of Venus even with the naked eye. Through a telescope you can clearly see how the appearance of the crescent of Venus changes. After the invention of the telescope, the observation of this particular phenomenon served as proof that all planets are spherical and visible due to reflected sunlight.

Moon phases

On a clear, cold autumn night you go outside. The Moon had just risen, a huge round orange Moon. A few days later, you notice that the moon is no longer as round. A few more days pass - the Moon has turned into a horned moon. After two weeks, the Moon disappears altogether.

Why does the Moon change shape?

What happened? Why does the Sun always turn its round sparkling face towards us, and the Moon has phases? The moon passes them regularly every month, sometimes increasing and sometimes decreasing, like a balloon that is being inflated and then deflated.

In reality, of course, the Moon always remains a ball, invariably hard and rocky. What actually changes is the amount of the illuminated surface of the Moon that we can see.

The Moon makes one revolution around its axis in almost the same time that it makes one revolution around the Earth (in 27/3 days), so the Moon almost always faces the Sun with only one side. But it is wrong to think that eternal night reigns on one side of the moon. Although slowly, the change of day and night still occurs.

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Why do the Moon and Sun change color? Description, photo and video

Why does the moon glow?

What we call moonlight is actually sunlight reflected by the gray, rocky lunar surface. The Moon moves with the Earth around the Sun and is illuminated by the Sun. As the Moon moves, we see either a larger or smaller part of the illuminated surface of the Moon, that is, the position of the Moon in relation to the Earth is changing all the time.

What we call the "phases" of the Moon are the angles at which we see the illuminated part of the Moon. When we see it completely, this position is called the full moon. When, after a few days, the Moon becomes “defective,” we already see part of its illuminated half (the first quarter after the full moon).

Since childhood, the idea has formed in our heads that the Sun can be seen during the day and the Moon at night. The sphere of “activity” of the heavenly bodies was clearly distributed. However, a strange fact is evident: quite often the night star is visible during the day. Paradox or just gaps in our astronomical knowledge? Definitely the second option. And in our article we will try to explain in simple language why the Moon is visible during the day.

Reasons for the visibility or invisibility of objects in the sky

Various objects in the field of view from the Earth are noticeable to varying degrees. The Sun is incomparably brighter against the background of the daytime sky than the Moon at night. At the same time, we remember that the distance from the satellite to the Earth is much smaller, cosmically smaller. Understanding this is important when we examine the question of why the Moon is visible during the day.

There is such a thing as brightness - stellar magnitude. In order for them to be clearly visible during daylight hours, their brightness must be much greater than that of the daytime sky. So, the clear sky during the day is 9.5, and the moon is 12.7. The excess is obvious, and therefore the satellite should be noticeable by all factors, although not in strong contrast with the background. This is the simplest and most understandable explanation for us, not astronomers, as to why the Moon is visible during the day.

When can the Moon and Sun be seen at the same time?

We have perfectly learned from childhood that the Moon revolves around the Earth, and the Earth revolves around the Sun. To this we must add that the planet also moves around its axis. The celestial bodies seem to be in a constant dance, changing positions. And this is extremely important to take into account when figuring out when and why the Moon is visible during the day.

Taking into account all the conditions, it is possible to see the Moon and the Sun together only on a full moon. Moonrise also coincides at this time. The rest of the time, the satellite should theoretically be visible during the day. But other factors also play a role here. The Moon is more visible in the daytime sky during periods when it approaches its full phase and its angular distance from the Sun is greater. In other phases, growing and aging, the side of the satellite illuminated by the Sun is small and turned towards it. Accordingly, the narrow strip of the young month will be extremely difficult to see during the day. This is why the Moon is not always visible during the day: sometimes it is simply difficult to notice.

Properties of the atmosphere and contrast of astronomical bodies

The atmosphere of our planet during the daytime is blue (we immediately imagine the appearance of a clear sky). Also, due to scattered particles of light from the Sun, it is bright. It is the brightness of the day that drowns out the brightness of the Moon. The latter, due to the atmosphere, could also be visible to us in blue, but the low contrast prevents this from happening. If the Moon appears in the sky during the day, it is most often a pale spot that is easy to miss. However, this did not stop astronomers from conducting their studies of the surface of the satellite even during daylight hours.

Thus, we understand that the light in the atmosphere of our planet makes it difficult to see the noticeable outline of the Moon, as at night. For a significant part of its cycle, the satellite is in a position where it is clearly visible near the Sun during the daytime. Therefore, the more pressing question is not why the Moon is visible during the day, but why it is not so clearly visible.

Experiments with photographs of the lunar surface

Despite the pale outline, the Moon is visible to the naked eye during the day. Astronomers could not miss this moment: since it can be seen without equipment, then what will happen if technology is used? Experiments began with photographing the surface of the Moon during the day. It must be said that their quality was quite good, considering the atmospheric conditions. The first such photograph was taken using a conventional digital camera attached to a telescope. The result was as expected: due to the low contrast of the Moon against the background of the daytime sky, its image was unclear.

The experiment was continued under the same conditions and with the same technique, but in black and white colors. The photo turned out to be somewhat more contrasty. To improve the image, we used the usual Photoshop. The processing made it look like one of the photographs taken during evening shooting. Thus, it became possible to see relief objects in the photo. It is noteworthy that both large craters (Grimaldi, Gassendi, Aristarchus) and smaller ones are clearly visible.

The experiments cited as an example with filming the lunar surface during the day prove that the satellite is not easy to see during daylight hours. It can even be explored from an astronomical perspective. We believe that the question of why the Moon is visible during the day has already received a completely clear answer.

conclusions

There are many mysteries for us in space, but humanity has managed to study the nearest objects to some extent. The night luminary, the satellite of the Earth, are objects of romantic views, accustomed to contemplating it only in the dark. However, the Moon can also be seen during the day, sharing the sky with the Sun.

In our article, we tried to understand in simple terms why the Moon can be seen during the day and what is the reason for the fact that sometimes we do not notice it. We hope that we have helped you expand your knowledge of the world around you.

The Moon's orbit around planet Earth takes about a month. In addition, it also moves around its axis. This process takes just over 27 days. Since the orbital movement and rotation around its axis occur simultaneously, the Moon is always directed towards the Earth with one side.

The Moon itself does not shine like the Sun. It only gives the impression that it is shining, 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 completely illuminated surface of the satellite, and from time to time only part of it is illuminated. That's why it seems to us that the Moon is changing its shape. But this is only a transformation of the star - phases that indicate that we can see its different 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. Such a Moon is not visible to us. Then comes a 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 its last quarter, then the cycle ends and starts all over again.

Earth and Moon

Does the Earth's movement around its axis coincide with the rotation periods of the Moon, or is it just the gravitational influence of one celestial body on another? Many inquisitive minds have sought the answer to this question.

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

And the question “why the Moon is different” has a simple answer: the Earth is subject to lunar gravity in different ways from different sides. The side facing the satellite is more affected than the opposite side.

As a result, different parts of the Earth move towards the side at different speeds. The surface, which is directed towards the Moon, swells, in the center the Earth moves less, and the opposite surface lags behind completely, 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 towards 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 that time there were only 20 hours in a day. It took the Moon only a few days to go around the Earth, and therefore were more pronounced. Over time, the satellite’s movement slows down, and in five billion years the Earth will rotate so slowly that it will itself be turned to the Moon with only one side, and there will be only 9 days in a year, not 365. It will make nine revolutions a year. Consequently, the year will not have 12 months, as it does now, but only 9, and each will have only one day.