Galileo was the first to observe the phases of Venus. He argued that the fact it exhibits a gibeous phase proves that it orbits the Sun and not the Earth. When Venus is closest to the Earth it is in its new phase and cannot be seen. When Venus is in its full phase it is at its most distant from the Earth but still cannot be seen as it is behind the Sun. Venus is brightest when it is 39 degrees from the Sun. This occurs 36 days before and after its full phase. When Venus is close to the Earth it has an angular diameter five times that of when it is furthest away.