Earth phase

File:Earth seasons 2021-2022.jpg, here viewed from geostationary orbit.]]

Among the most prominent features of the Moon's sky is Earth. Earth's angular diameter (1.9°) is four times the Moon's as seen from Earth, although because the Moon's orbit is eccentric, Earth's apparent size in the sky varies by about 5% either way (ranging between 1.8° and 2.0° in diameter). Earth shows phases, just like the Moon does for terrestrial observers. The phases, however, are opposite; when the terrestrial observer sees the full Moon, the lunar observer sees a "new Earth", and vice versa. Earth's albedo is three times as high as that of the Moon (due in part to its whitish cloud cover), and coupled with the wider area, the full Earth glows over 50 times brighter than the full Moon at zenith does for the terrestrial observer. This Earth light reflected on the Moon's un-sunlit half is bright enough to be visible from Earth, even to the unaided eye – a phenomenon known as earthshine.

As a result of the Moon's synchronous rotation, one side of the Moon (the "near side") is permanently turned towards Earth, and the other side, the "far side", mostly cannot be seen from Earth. This means, conversely, that Earth can be seen only from the near side of the Moon and would always be invisible from the far side. Earth is seen from the lunar surface to rotate, with a period of approximately one Earth day (differing slightly due to the Moon's orbital motion).

If the Moon's rotation were purely synchronous, Earth would not have any noticeable movement in the Moon's sky. However, due to the Moon's libration, Earth does perform a slow and complex wobbling movement. Once a month, as seen from the Moon, Earth traces out an approximate oval 18° in diameter. The exact shape and orientation of this oval depend on one's location on the Moon. As a result, near the boundary of the near and far sides of the Moon, Earth is sometimes below the horizon and sometimes above it.

To be aware, although genuine photographs of Earth viewed from the Moon exist, many from NASA, some photographs shared on social media, that are purported to be Earth viewed from the Moon, may not be real.

The Blue Marble (remastered).jpg|{{center|Full}}

AS08-16-2593 remastered.jpg|{{center|Gibbous}}

NASA-Apollo8-Dec24-Earthrise.jpg|{{center|Low-illumination gibbous}}

AS12-50-7351 (21080121634).jpg|{{center|Very low-illumination gibbous}}

Apollo 13 - View of Earth.jpg|{{center|Half}}

First View of Earth from Moon - reprocessed wide.jpg|{{center|High-illumination crescent}}

Waning crescent earth seen from the moon.jpg|{{center|Crescent}}

Crescent Earth, Apollo 17.jpg|{{center|Low-illumination crescent}}

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{{div col|colwidth=30em}}

• Earthrise
• Extraterrestrial sky
• List of first images of Earth from space
• List of notable images of Earth from space
• Lunar phase
• Overview effect
• Pale Blue Dot
• Pale Orange Dot (Early Earth)
• Planetary phase
• The Blue Marble
• The Day the Earth Smiled

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{{reflist|30em|refs=

{{cite web |author=Staff |title=Changing Earth phases, seen from the moon |url=https://earthsky.org/space/what-would-earth-look-like-from-the-moon |date=21 June 2008 |work=Earth & Sky |accessdate=30 June 2019}}

{{cite news |author=Staff |title=The Phases of Earth |url=https://futurism.com/the-phases-of-earth |date=13 March 2013 |work=Futurism.com |accessdate=30 June 2019 }}

{{cite news |last=Gannon |first=Megan |title=If You're On the Moon, Does the Earth Appear to Go Through Phases? |url=https://www.livescience.com/65831-earth-phases-from-moon.html |date=30 June 2019 |work=Live Science |accessdate=30 June 2019 }}

{{cite news |last=King |first=Bob |title=Observing Earth from the Moon |url=https://www.skyandtelescope.com/astronomy-blogs/explore-night-bob-king/observing-earth-from-the-moon/ |date=17 October 2018 |work=Sky & Telescope |accessdate=30 June 2019 }}

{{cite web |last=Evon |first=Dan |title=Is This a Real Photo of the Earth from the Moon? - Genuine photographs showing the Earth from the moon exist, many from NASA. |url=https://www.snopes.com/fact-check/image-of-earth-from-moon/ |date=15 July 2019 |work=Snopes |accessdate=17 July 2019 }}

{{cite web |author=Staff |title=If you are on the moon, does the Earth have phases similar to moon phases? Would they be the same or reversed? |url=http://scienceline.ucsb.edu/getkey.php?key=3133 |date=15 July 1999 |work=University of California, Santa Barbara |accessdate=1 July 2019 }}

{{cite web |last=Cain |first=Fraser |title=What Does Earth Look Like From the Moon? |url=https://www.universetoday.com/115235/what-does-earth-look-like-from-the-moon/ |date=13 October 2014 |work=Universe Today |accessdate=1 July 2019 }}

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• [https://www.compadre.org/osp/items/detail.cfm?ID=13394 Earth phases – model simulation program]
• {{YouTube|YQfm2icwtDk|Video (00:36) – Earth phases seen from the Moon}}
• {{YouTube|-HgHEO0DUig|Video (02:05) – Earth phases seen from the Moon}}

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phase

Category:Observational astronomy