dipper@utastro.UUCP (Debbie Byrd) (11/07/86)
There's a transit of the planet Mercury coming up -- which we'll talk about right after this. November 7 When Mercury Transits the Sun This past Wednesday, the planet Venus reached inferior conjunction. On that day, this planet -- whose orbit lies inward from that of Earth -- rushed between our world and the sun. Next week, the inner planet Mercury will do the same thing. It will pass between us and the sun in its smaller orbit -- moving at 30 miles per second compared to our 18. But, while Venus passed south of the sun as seen from Earth, Mercury will pass directly in front of the sun from our point of view. Those turned in the sun's direction when this event occurs will see a "transit" of Mercury across the disk of the sun. It will be the first transit of Mercury since 1973. As luck would have it, the transit will not be observable from North or South America, with the exception of southwestern Alaska. It will be nighttime for most of us when the transit takes place. People who want to see it will need telescopes -- because Mercury is so small compared to the sun -- and they'll need special filters to block the sun's blinding rays. But today is a special date with regard to mercurian transits -- because the first observation of a transit of Mercury was made on today's date, November 7th, in the year 1631. Pierre Gassendi used a projection technique to watch during the five hours or so that Mercury takes to cross in front of the disk of the sun. It's said that he nearly missed seeing the transit -- because he had expected that the planet would look much larger than it did. So that's a transit of Mercury -- coming up next week -- during the night, our time, of November 12. We'll talk more about it then. Script by Deborah Byrd. (c) Copyright 1985, 1986 McDonald Observatory, University of Texas at Austin