November 2006

by Deane Morrison

In June 2004 Venus made headlines by sailing gracefully across the face of the sun in a spectacle astronomers call a "transit." This month Mercury follows suit¿but with a few differences.

One nice thing about Mercury's transit is that it will happen during the afternoon for us in the Midwest--not the crack of dawn, as Venus's transit. It begins at 1:12 p.m. CST on the 8th, the moment Mercury first makes contact with the sun's edge. The planet will be halfway across the sun's face at 3:41 p.m., and the transit will end at 6:10 p.m. But the sun will go down a good hour before that, so people watching at sunset will see star and planet set together. As usual when viewing the sun, the transit must only be watched through a telescope with a proper solar filter to prevent eye damage.

Another difference from 2004 is that Mercury will appear much smaller than Venus. For one thing, it really is much smaller; its diameter is only 3,032 miles, compared to 7,521 miles for Venus. Also, it is farther from us than Venus, which reduces its apparent size. But that just increases the satisfaction of finding it against the huge solar face.

Transits of Mercury occur in May and November because those are the times when Mercury crosses the plane of Earth's orbit. But transits don't happen every year, only in years when Earth is lined up with Mercury and the sun at the moment Mercury crosses our orbital plane. The next transit of Mercury occurs 10 years hence, on May 9, 2016.

After this year's crossing, Mercury enters the morning sky and makes its best showing in the east an hour or so before dawn on the 24th and 25th.

This year could be a good one for the Leonid meteor shower, but no one is sure. The best times to look will be in the predawn hours of the 17th, 18th and 19th. The meteors radiate from the head of Leo, inside a curving line of stars known as the Sickle. No bright planets greet the viewer at nightfall this month. The only bright evening planet is Saturn, which rises around midnight on the 1st but appears shortly after 10 p.m. by the end of November. The planet isn't as bright as it's been lately, thanks to the unfavorable tipping of its rings. But Saturn is in a great position to cast its shadow on the rings, giving depth to the world of this lovly planet. Watch it slowly close in on Regulus, the brightest star in Leo.

The full moon of November is known as the frosty moon or the beaver moon, for the busy rodents now getting their lodges ready for the winter. This year, being the next full moon after October's harvest moon, it is also the hunter's moon. That name refers to the open fields of post-harvest, which offer less cover for game. Whatever you call it, the full moon comes at 6:58 a.m. on the 5th, about 15 minutes before it sets in the west.

The Milky Way arches across the sky from east to west in November. Late in the evening¿but getting earlier every night¿you'll see the familiar form of Orion rising just under the eastern end of the beautiful river of stars.

The University of Minnesota, Twin Cities, department of astronomy offers free public viewing Friday nights during the winter when the sky is at least half clear. Check the schedule at http://www.astro.umn.edu/outreach/pubnight/ and in any case call (612) 626-0034 an hour before each session to verify that a session will be held. There will be no viewing on the 24th (the day after Thanksgiving) this year. Viewings are held on the roof of the Tate Laboratory of Physics, 116 Church St. S.E., Minneapolis.