Atmosphere of the Moon and Moon Space
Since the mass of the moon is negligible, the gas shell around it must be very rarefied, i.e. practically absent. The main components of the gas shell were hydrogen, helium, neon, and argon. The highest density is observed at night and corresponds to about 2 · 105 cm – 3. in the daytime, the gas concentration drops to 104 cm – 3 in terms of density at the surface. Therefore, we can speak with good reason about the presence of some kind of gas shell around the moon.
The moon has practically no global magnetic field of a dipole nature. This circumstance explains the peculiarities of the interaction of the Moon with the stream of charged particles of the solar wind, which consists mainly of protons and electrons with the addition of ionized helium and other heavier elements with different degrees of ionization. The moon is a non-magnetic, relatively non-conductive and cold dielectric sphere. Therefore, the Moon absorbs the plasma of the solar wind and streams of energy particles freely falling on the lunar surface.
Observations found a constant excess background of the brightness of the sky. It is believed that such a phenomenon can be associated with the presence of a scattered dust layer about 103 km thick above the surface with a particle size of 70 μm and a concentration of 7 · 10–10 cm – 3. the moon is, as it were, shrouded in a transparent dust cloud, having a length comparable to the radius of the lunar ball.
The movement of the moon.
The moon moves around the earth with an average speed of 1.02 km / s in an approximately elliptical orbit in the same direction as the vast majority of other bodies of the solar system, i.e. counterclockwise, have sat down to look at the moon’s orbit from the North Pole of the world. The semimajor axis of the Moon’s orbit, equal to the average distance between the centers of the Earth and the Moon, is 384,400 km (approximately 60 Earth radii). Due to the ellipticity of the orbit and disturbances, the distance to the moon varies between 356,400 and 406,800 km. The period of revolution of the Moon around the Earth, the so-called sidereal (stellar) month, is 27.32166 days, but is subject to small fluctuations and a very small secular reduction.
In the process of its movement in space, the Moon is influenced mainly by two bodies — the Earth and the Sun. At the same time, solar attraction is two times stronger than Earth. Therefore, the Earth and the Moon revolve around the Sun, being nearby from each other.
The rotation of the moon around its own axis is described by the three Cassini laws. The moon rotates at a constant angular velocity in the direction of the Earth’s revolution, and the period of the Moon’s rotation is equal to its orbital period. The equality of the periods of the axial and geocentric rotation of the Moon creates a feature of the Earth-Moon system, in which the same hemisphere of the satellite — the visible side of the Moon — is constantly facing our planet. The actual rotation of the moon is accompanied by small fluctuations of a nutational nature. These small vibrations are called physical libration.
The lunar axis of rotation makes an almost right angle with the ecliptic plane (88 °, 5), so the lunar sunny days are divided into equal intervals of dark and light time, regardless of the position of the moon. There are no observed astronomical signs of seasonal changes on the lunar surface.
The various visible forms of the moon are called its phases. The full cycle of phases ends and begins to repeat every 29.59 days. Not being self-luminous, the Moon is visible only in the part where the sun’s rays or rays reflected by the Earth fall. This explains the phases of the moon. Because of the remoteness of the sun, the sun’s rays falling on the moon are almost parallel and always illuminate exactly half of the lunar ball; the other half remains dark. Part of the bright hemisphere and part of the dark are usually facing the Earth, therefore the Moon most often seems to us an incomplete circle. The line separating the dark part of the moon’s disk from the light is called a terminator and is always a semi-ellipse. The angle between the directions from the Sun to the Moon and from the Moon to the Earth is called the phase angle. There are four main phases of the moon, which gradually pass one into another in the following sequence: new moon, first quarter, full moon and last quarter.
Each month, the Moon, moving in orbit, passes between the Earth and the Sun and faces us on the dark side, at this time a new moon occurs. 1 – 2 days after this, a narrow bright sickle of the young Moon appears in the western part of the sky. The rest of the lunar disk is at this time poorly lit by the Earth, turned to the Moon with its daytime hemisphere. Then people say that “the new moon is in the hands of the old.” The lunar crescent, convex to the Sun, is gradually expanding from day to day. 7 days after the new moon, the Moon takes the form of a semicircle and moves away from the Sun by 900, the first quarter comes when exactly half of the moon’s disk is illuminated and the terminator, that is, the dividing line of the light and dark sides, becomes straight – the diameter of the lunar disk.