dipper@utastro.UUCP (Debbie Byrd) (11/12/86)
What happens when Mercury passes in front of the sun -- after this. November 12 More Transit of Mercury Today -- actually, tonight for most of us -- the planet Mercury will transit the sun. That means it will cross in front of the the face of the sun as seen from Earth. The sun won't be up for most of us. But the entire transit will be seen from India, Southeast Asia, China, Japan, Indonesia, Australia and New Zealand. Observers in those locations who are equipped with telescopes and safe solar filters will witness the tiny black dot of Mercury moving across the brilliant face of the sun. The whole event will take approximately five hours. An interesting phenomena occurs during transits as the little disk of the planet comes wholly inside the disk of the sun. Then the so-called black drop effect is seen, when the planet will seem to be attached to the edge of the sun by a thin column or thread. That illusion ends when the thread appears to break, and the planet is entirely surrounded by sunlight. Since Mercury and Venus are the only planets orbiting inward from Earth, they are the only ones we ever see transiting the sun. While transits of Mercury occur 13 times each century, transits of Venus are much more rare. The last one was on December 6, 1882. The next one will be on June 8, 2004. If you were on Mars, however, you'd occasionally have the pleasure of seeing Earth transit the sun! The last transit of Earth as seen from Mars in this century took place on May 11, 1984. If there had been astronomers on Mars on that date, and if they'd had good weather, telescopes, and filters to dim the blinding sunlight, they could have seen Earth as a black dot moving across the sun's disk. Script by Deborah Byrd. (c) Copyright 1985, 1986 McDonald Observatory, University of Texas at Austin