The beginners in astronomy know that motion of Moon on sky is not so simple, as say the Sun or stars are. The reason is that the visible motion of the Moon consists of three independent basic motions: rotations of Earth around the axis, rotation of Moon round Earth and rotation of Earth round the Sun. Motion of Moon is on an elliptic orbit, with a period in 27,32 twenty-four hours. Exactly for the same time it applies about the axis. Therefore Moon seems always facing Earth one side. This phenomenon is not unique - almost all large moons of the sunny system move. If all the track of the Moon on the sky (360°) is to divide its appeals (27,32 twenty-four hours) into a period, then we get: displacement of Moon in relation to stars for twenty-four hours - about 13°, or about 0°, 5 for 1 hour. The visible angular diameter of lunar disk is equal to approximately 0°, 5. So, noticing position of Moon among stars, we will see even with a naked eye, that for one hour it is moved to distance equal to the diameter of its disk. Moon is moving among stars in direction west- east (from right to left) in the motion round Earth. But its day's motion (together with the vault of heaven) takes place, naturally, east - westward. If we go out of doors at the same time two evenings, then we will notice that in relation to stars Moon is already considerably more east (more left), than the day before. Naturally, that it ascends later, than in a previous evening (approximately on 50 minutes). Craters and creeks on the surface of Moon are the best visible in the full moon. We see that part of lunar surface is presently lighted up by the Sun. Therefore the type of Moon on sky (stake of the lunar surface lighted up in the moment of supervision) changes constantly, or, as they say astronomers, there is some change of lunar phases. When at motion Moon round Earth, it appears between a planet and the Sun, and then to us an unlit, dark lunar hemisphere is turned. Moon at this time is invisible. Over-the-horizon it calls together with the Sun. It is the phase of new moon. It seems during the period of the new moon the sun must it each time, i.e. there must be the sunny eclipse. However it takes place far not always. The point is that the lunar orbit is inclined 5 degrees to the plane of earth orbit. Hence, the Moon in its new phase passes the sky either some higher or some below than the Sun does.
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