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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