It is obvious that solar eclipses can occur only in the new moon phase.

It is obvious that solar eclipses can occur only in the new moon phase.

The angular velocity of the Moon per day is from 11 ° to 15 °.

The period of time during which the Moon, describing a complete circle in the celestial sphere, returns to the same point, is called the sidereal or stellar moon (from the Latin «sidus» – «star»). The sidereal month is equal to 27 1/3 of the day.

Careful study of the apparent motion of the Moon among the stars with its path on the star map leads to the conclusion that the Moon moves in the celestial sphere in a large circle inclined to the ecliptic by about 5 °, which is almost equal to 10 of its angular diameters. This circle intersects the ecliptic at two diametrically opposite points, called the nodes of the lunar orbit. The node in which the Moon, moving in the sky, descends under the ecliptic and deviates to the south, is called descending, and the one in which after 13.6 days it rises above the ecliptic and deviates to the north, is called ascending.

It is easy to see that the conditions of visibility of the Moon at different times of the year are very different. In summer, the full moon is low and short in the sky, and in winter it shines high and long, because the arc of the ecliptic in the night summer sky lies below the celestial equator, and in winter – above it. The lowest height of the Moon in summer for latitude φ = 50 ° can be 11 °, its highest height in winter for latitude φ = 50 ° can be 68 °.

Phases of the Moon. The surface of the Moon glows with reflected sunlight, so its appearance changes depending on its position relative to the Sun. Such a change in the appearance of the Moon for the observer on Earth is called the phases of the Moon. There are four main phases: the new moon – 1, the first quarter – 3, the full (full moon) – 5, the third (last) quarter – 7.

Examining the position of the Moon among the stars at the time of repetition of the same phase, we can conclude that the same phases of the Moon are repeated approximately every S = 29.5 days, but they occur at different points in the lunar orbit – in each subsequent month 30 ° east. with the previous one.

The time interval S between the two phases of the Moon of the same name is called the synodic moon (from the Greek «synodos» – «convergence» means the convergence of the new moon with the sun).

As we can see, the duration of the synodic month is longer than the sidereal month. It is easy to see why this is so. Let the full moon at the initial moment be near some star. In 27.3 days he will be close to her again. However, during this time the Earth will shift in its orbit (and, accordingly, the Sun in the celestial sphere) by an angle of about 27.3 °. Therefore, to take the same position relative to the Sun and be full again, the Moon must move for another 2¼ days. This value is exactly the difference between the sidereal months.

Eclipse of the Sun and Moon. The Earth and the Moon, illuminated by the Sun, cast shadows in the form of cones in the opposite direction from the Sun. The cone of the Earth’s shadow is longer than the moon, and its diameter at a distance of the Moon exceeds the diameter of the Moon by more than 2.5 times. Moving around the Earth, the Moon twice a month is on the Earth-Sun line. At such moments, a solar or lunar eclipse may occur.

A solar eclipse occurs when the shadow of the moon falls on the Earth’s surface. It is observed differently at different points on the earth’s surface. The Sun’s disk will be completely closed only to the observer, who is inside the lunar shadow, the average diameter of which on the Earth’s surface is 100 km. A total solar eclipse will be observed in this narrow area.

In areas of the earth’s surface where the penumbra falls from the moon, inside the so-called lunar penumbra, there will be a partial solar eclipse.

Since the distance of the Moon from the Earth due to the ellipticity of its orbit varies from 405,500 km to 363,300 km, and the length of the cone of its total shadow is 374,000 km, sometimes the top of this cone does not reach the Earth’s surface … In this case, the edges of the solar disk will remain open and will form a thin shiny ring around the dark disk of the moon. This eclipse is called a ring.

In different parts of the Earth, solar eclipses occur at different times. Due to the movement of the Moon around the Earth and the rotation of the Earth around the axis, the shadow from the Moon moves along the Earth’s surface from about west to east, forming a band several thousand kilometers long and a maximum width of 270 km … The total eclipse phase, when the Sun is completely covered by the Moon’s disk, lasts no more than 7.5 minutes.

Together with the partial phases, when the Moon is just approaching the Sun or rising from its disk, a solar eclipse can last more than two hours. It is obvious that solar eclipses can occur only in the new moon phase.

A lunar eclipse occurs when the Moon falls into a cone of shadow cast by the Earth. Because during an eclipse the Moon is actually deprived of sunlight, the lunar eclipse is visible throughout the nocturnal hemisphere of the Earth and for all points of this hemisphere begins and ends simultaneously.

The complete phase of the eclipse can last up to 1 hour. 40 minutes, and the entire lunar eclipse lasts more than three hours. Obviously, lunar eclipses can only occur during a full moon.

If the plane of the lunar orbit coincided with the plane of the ecliptic, solar and lunar eclipses would be observed every synodic month. But it is inclined to the plane of the ecliptic at an angle of 5 °, so the Moon can pass either above or below the disk of the Sun or the cone of the Earth’s shadow.

For a solar or lunar eclipse to occur, it is necessary that the Moon in the phase of the new moon or in full moon was near one of the nodes of its orbit, ie near the ecliptic.

Every year there are two solar eclipses; under good circumstances, there may be as many as five. As for lunar eclipses, it is estimated that there may be two or three a year, or not at all. Thus, the minimum number of eclipses per year is two (both solar), the maximum is seven (five solar and two lunar, or four solar and three lunar).

The sequence of eclipses is repeated almost exactly in the same order after some period of time, called saros (from the Egyptian – «repetition»). Saros, known long before our era, is 18 years and 10.3 or 11.3 days (depending on how many leap years there were in the period).

Repetition of the sequence of solar and lunar eclipses Occurs due to the repetition of the mutual position of the Sun, Moon and the nodes of the lunar orbit in the celestial sphere.

During each saros there are 43 solar eclipses and 25-29 lunar ones. At a certain longitude, the same eclipse is repeated through three saros. And at a particular point on Earth, a total solar eclipse occurs on average every 300 years.


Planet Saturn: physical characteristics. Abstract

Saturn is the second giant planet and the sixth largest planet in the solar system. Almost in all respects similar to Jupiter, it revolves around the Sun with a period of 29.5 Earth years at a distance of about 9.5 a. at.

Stellar time on Saturn lasts 10 hours. 45 min Due to its rapid rotation, it is flattened at the poles: the polar radius of the planet is smaller than the equatorial. The periods of its rotation in different latitudes are not the same. Saturn’s mass is 95 times greater than Earth’s mass, and gravity is 1.12 times greater than Earth’s.

Saturn has a surprisingly low density, lower than the density of water – only 0.7 g / cm3. And if there was such a huge ocean of water, where you could dive Saturn, he would not have drowned. Such a low density suggests that, like the other giant planets, Saturn consists mainly of hydrogen and helium.

Because Saturn is 9.5 times farther from the Sun than Earth, it receives 90 times less heat per unit area than it does. According to calculations, the temperature of the outer layer of the cloud cover should be 80K, in fact, the temperature of the planet’s atmosphere is 90K. Thus, Saturn, like Jupiter, is in a state of slow compression. On the yellowish disk, some details of the upper layers of Saturn’s atmosphere are much weaker than in Jupiter.

However, with the equatorial dark stripes are visible quite well. It is also noticeable that the subpolar zones seem to be slightly reduced. In addition, from time to time there are light and dark spots, due to which the period of Saturn’s rotation was determined. In the upper layers of the cloud cover, strong winds are observed, the speed of which in the equatorial zone reaches 110 m / s.

Saturn, like Jupiter, has a magnetic field, radiation belts, and is a source of radiation.

Among the giant planets, Saturn is the most interesting planet in the solar system. A wide, completely flat ring surrounds the equator of the planet, like the hat of its rat. It is located at an angle to the circle around which Saturn orbits the Sun in 29.5 years. Therefore, depending on the position of Saturn in its path, the ring returns to us on one side or the other. Every 15 years it becomes an edge to us, and then it can not be seen even in the most powerful telescopes, which means that the ring is very thin and its thickness does not exceed 10-15 km.

The famous astronomer Galileo discovered in 1610 that Saturn was surrounded by something. But his telescope was too weak, so Galileo could not make out what he saw around Saturn. Only half a century later, the Dutch scientist Huygens was able to see that this is actually a flat ring that surrounds the planet, and nowhere touches it. The study of Saturn with the help of more advanced telescopes showed that the ring splits into three parts, which form like three independent rings nested in each other.

The outer ring is separated from the middle by a dark gap – a narrow black slit. The middle ring is brighter than the outer one. From the middle, a translucent third ring fits tightly to it. What are these interesting rings? Maybe these are really solid little pads? No it is not. Prominent scientists – the English physicist Maxwell and the Russian woman mathematician SV Kovalevskaya proved by their calculations that a solid and solid ring of this size could not exist: it would be instantly destroyed due to differences in gravity for different parts of it.

Prominent n astrophysicist AA Belopolsky close observations of Saturn confirmed that the ring is not really continuous.