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Phases of Venus
The phases of the planet Venus are the different variations of lighting seen on the planet's surface, similar to lunar phases. The first recorded observations of them were telescopic observations by Galileo Galilei in 1610. Although the extreme crescent phase of Venus has been observed with the naked eyes, there are no indisputable historical pre-telescopic records of it being observed.〔
==Observation==
The Phases of Venus result from the planet's orbit around the Sun inside the Earth's orbit giving the telescopic observer a sequence of progressive lighting similar in appearance to the moon's phases. It presents a ''full'' image when it is on the opposite side of the Sun. It shows a ''quarter phase'' when it is at its maximum elongation from the Sun. Venus presents a ''thin crescent'' in telescopic views as it comes around to the near side between the Earth and the Sun and presents its ''new phase'' when it is between the Earth and the Sun. Since the planet has an atmosphere it can be seen at ''new'' in a telescope by the halo of light refracted around the planet. The full cycle from ''new'' to ''full'' to ''new'' again takes 584 days (the time it takes Venus to overtake the Earth in its orbit). The planet also changes in apparent size from 9.9 arc seconds at ''full'' (superior conjunction) up to a maximum of 68 arc seconds at ''new'' (inferior conjunction).〔 Venus reaches its greatest brilliancy (magnitude) -4.5 when it is an intermediate crescent shape at the point in its orbit when it is 68 million kilometers away from the Earth (a combination of its closeness and the fact that it is 28% illuminated).〔(souledout.org - Venus Has Phases ... Like the Moon )〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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