What causes Venus to have phases like the moon?
It was Galileo who first saw that Venus has phases like the moon. He figured out that this happens because Venus is closer than the earth is to the sun. The sister planets swing around and around their orbits, but Venus has the inside track: It is forever overtaking the earth, passing it and swooping around to the opposite side of the sun to start the heavenly game of tag all over again. Half of Venus, of course, is always in daylight, while the other half is in the shadows of night. The dark side is invisible to us, and we see only where sunshine strikes the golden planet. When Venus is on the opposite side of the sun, we see the whole daylight side. This is its full moon phase. When Venus comes between us and the sun, its dark side is facing us and our neighbor planet is invisible. When it is on the east or west of the sun, we see part of the day side and part of the night side. Venus passes through quarter and gibbous or half phases. Last January, the Sister planets were on opposite
