<P> 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 . </P> <P> 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 magnitude of − 4.5 when it is an intermediate crescent shape at the point in its orbit, when it is 68 million km away from the Earth (a combination of its closeness and the fact that it is 28% illuminated). </P> <P> The first known observations of the full planetary phases of Venus were by Galileo at the end of 1610 (though not published until 1613 in the Letters on Sunspots). Using a telescope, Galileo was able to observe Venus going through a full set of phases, something prohibited by the Ptolemaic system . (The Ptolemaic system would never allow Venus to be fully lit from the perspective of the Earth, as this would require it to be on the far side of the sun, which is impossible if Venus's orbit in its entirety is between the Earth and the sun, as the Ptolemaic system requires). This observation essentially ruled out the Ptolemaic system, and was compatible only with the Copernican system and the Tychonic system and other geoheliocentric models such as the Capellan and Riccioli's extended Capellan model . </P>

Venus full phase occurs when venus is at