Earth phase - the form of the illuminated part of the Earth’s surface when observed from the moon (or from another object). From the Moon, the phases of the Earth change gradually and cyclically with a period equal to the synodic lunar month (about 29.53 days), with which the location of the Earth and the Moon in orbit around the Sun changes. [1] [2] [3] [4] [5] [6]
Overview
Among the brightest objects in the moonlit sky is Earth. The angular diameter of the Earth (1.9 °) is 4 times the angular diameter of the moon in the earth's sky. But due to the eccentricity of the lunar orbit, the apparent size of the Earth in the sky of the moon varies by 5% (from 1.8 ° to 2.0 ° in diameter). The earth can also be seen in different phases, like the moon for the earth observer. The phases, however, are the opposite: when the earth observer sees the full moon, the moon observes the Earth unlit (analogue of the new moon), and vice versa. The Earth's albedo is three times higher than the moon's albedo (due to the presence of cloud cover), which, combined with a large angular size, gives 50 times more light from the full Earth than from the full Moon. Light from the Earth, reflected by an unlit lunar surface, is visible on Earth even with the naked eye.
Due to the synchronous rotation of the moon, one of its sides is always turned towards the Earth, and the other is mostly inaccessible for observation from the Earth. It also means that the Earth can be observed only on one side of the moon.
If the rotation of the moon was completely synchronous, the Earth would not make noticeable movements in the sky of the moon. However, due to the librations of the moon, the Earth describes a slow and complex oscillatory motion. During a month when observing from the moon, the Earth describes an oval with a diameter of 18 °. The exact shape and orientation of this oval depends on the position of the observer on the moon. As a result, near the border of the near and far sides of the Moon, the Earth can be both above the horizon and below it.
Lunar Eclipses
Earth and the Sun in the sky of the Moon can sometimes be near, which can cause eclipses. In this case, a lunar eclipse will be observed on Earth, at which the Moon passes through the shadow of the Earth. In this case, a solar eclipse will be observed on the Moon, at which the Sun will pass beyond the Earth. Since the apparent diameter of the Earth is 4 times larger than the visible diameter of the Sun, for the lunar observer the Sun will be hidden by the Earth for several hours. The Earth’s atmosphere is visible as a reddish ring. During the Apollo 15 mission, an attempt was made to use the lunar rover camera to observe such an eclipse, but after the astronauts returned to Earth, the camera or its power source failed. [7]
Earthly solar eclipses for observers on the Moon will not look very spectacular, since the lunar shadow passes only along a small fraction of the Earth’s surface. The blurry dark spot will be poorly visible. A comparable effect is exerted by the shadow of a golf ball falling on an object at a distance of 5 meters. A telescope from the moon could distinguish between shadow and partial shade.
Thus, if an eclipse of some type occurs on the Earth, an eclipse of another type also occurs on the Moon at this moment. Eclipses themselves occur at a time when the Sun, Moon and Earth are on the same straight line, that is, in syzygy .
Earth Phases
- Earth Phases
- Full phase
- Phase 3/4
- Half disc lit
- Half disc lit
- Half disc lit
- Growing phase
- Growing phase
- Growing phase
Notes
- ↑ Gannon, Megan . If You're On the Moon, Does the Earth Appear to Go Through Phases? , Live Science (June 30, 2019). Date of treatment June 30, 2019.
- ↑ Staff . The Phases of Earth , Futurism.com (March 13, 2013). Date of treatment June 30, 2019.
- ↑ Staff. Changing Earth phases, seen from the moon . Earth & Sky (June 21, 2008). Date of treatment June 30, 2019.
- ↑ King, Bob Observing Earth from the Moon . Sky & Telescope (October 17, 2018). Date of treatment June 30, 2019.
- ↑ Staff. If you are on the moon, does the Earth have phases similar to moon phases? Would they be the same or reversed? . University of California, Santa Barbara (July 15, 1999). Date of treatment July 1, 2019.
- ↑ Cain, Fraser What Does Earth Look Like From the Moon? . Universe Today (October 13, 2014). Date of treatment July 1, 2019.
- ↑ Jones, Eric M. Return to Orbit . NASA (June 11, 2013). Date of treatment June 30, 2019.