# From the surface of which planet in the solar system will the Earth look brightest, and what will it have at the same time?

From the surface of which planet in the solar system will the Earth look brightest, and what will it have at the same time? The brightness of the full Earth on the Moon is -17m.

The brightness of the Earth will be the higher, the closer it is to the observation point, and the more phase it will have. Therefore, we may not even consider giant planets that are very far from the Earth. Mars may come close enough to the Earth during its great oppositions, but at this time the Earth will be turned towards it by its unlit side, and its brilliance will be far from maximum. Near its upper conjunction with the Sun, the Earth will have an almost complete phase, but again will be removed by more than 2 AU. Much closer, the Earth in full phase can be located to Mercury and Venus during its oppositions on these planets. But Venus is shrouded in a dense cloud layer, and from its surface we will not be able to see the Earth, no matter how bright it is. As a result, the Earth looks brightest from the surface of Mercury when both planets are on the same side of the Sun. If Mercury is located near the aphelion point of its elongated orbit, then its distance from the Sun is 0.47 AU, and from the Earth – about 0.53 AU. or 79.3 million km. If from the distance of the Moon in 384400 km the Earth has a brightness of –17m, then from the distance of Mercury it will be equal to m = –17 + 5 lg (79300000/384400) = –5.4.

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