dipper@utastro.UUCP (Debbie Byrd) (11/05/86)
Venus is between us and the sun today. More -- after this. November 5 Venus at Inferior Conjunction The planet Venus orbits inward from Earth -- and today it rushes between us and the sun. That means we won't see Venus anywhere in our sky around now. Instead, the planet rises when the sun does -- and travels across the sky throughout the day -- invisible in the solar glare. Earth moves around the sun at 18 miles per second. But Venus, being closer to the sun, travels faster -- it moves about 21 miles for each second ticking by on our clocks. Venus returns to inferior conjuction -- to that unseen location between the Earth and sun -- every 584 days. In the 1960s, the idea came into being that Venus was gravitationally locked to Earth -- that it showed the same face to Earth at every inferior conjunction. It would be a similar situation to that of the moon -- which ALWAYS keeps one face toward our world. The rotation period of Venus was thought to be precisely 243.16 days. As seen from Earth, the planet was thought to spin on its axis four times between inferior conjuctions. Then in 1979, astronomers announced the results of an analysis of fourteen years of radar observations of Venus. They showed that the rotation period of Venus is actually a few hours off from the exact rotation period required if the planet were to show the same face to Earth at each inferior conjunction. So it seems that Venus isn't exactly locked to Earth, after all. But, since the numbers are so close, the two worlds may be moving toward or away from a gravitational lock. And the question remains -- can two such small worlds, located relatively far apart, become gravitationally locked to each other? Script by Deborah Byrd. (c) Copyright 1985, 1986 McDonald Observatory, University of Texas at Austin