dipper@utastro.UUCP (Debbie Byrd) (11/11/86)
A transit of Mercury tomorrow -- more after this. November 11 Transit of Mercury Here's a special event for the innermost planet, Mercury. Tomorrow it passes between the Earth and sun -- which isn't unusual in itself -- but it's special tomorrow because Mercury will cross directly in front of the sun from our point of view. When Mercury passes in front of the sun's disk, we have what astronomers call a transit of Mercury. A transit isn't easy to observe. You need a telescope and special filters to dim the sun's light. But if you could see tomorrow's transit, you'd be able to watch the tiny disk of Mercury crossing in front of the larger disk of the sun. The whole event will take about five hours. If the orbit of Mercury lay in the same plane as that of the Earth, the planet would be seen crossing the disk of the sun three times every year. That's how often this innermost planet reaches inferior conjunction, when it is between the Earth and sun. But Mercury's orbit is very inclined to that of Earth. So mercurian transits occur on the average about thirteen times each century, always in May or November. Tomorrow's transit of Mercury will be seen mainly from Earth's eastern hemisphere. Unless you're in that hemisphere, or in southwestern Alaska or Hawaii tomorrow, you won't see Mercury until about the last 10 days of November. Then, to make things up to those of us who have to miss the transit, the planet will come on the scene for a wonderful apparition in the predawn sky. Look for Mercury in the east-southeast, to the lower left of Venus, beginning around November 21st. By the end of the month, the planet will be at greatest elongation, its farthest point from the sun on the dome of our sky. Script by Deborah Byrd. (c) Copyright 1985, 1986 McDonald Observatory, University of Texas at Austin