It is not very often that we have the opportunity to get a good glimpse of Mercury. The closest planet to the Sun does not stray far from its home star in our skies. Because Mercury lies between Earth and the Sun, it can never appear opposite the sun in our sky. Therefore, all our best glimpses of Mercury occur when it is at what is called greatest elongation. Greatest elongation refers to the angle between the Sun and a planet as seen from Earth. When the greatest elongation occurs before sunrise, as happens this November 2006, it is called the greatest western elongation. If it were after sunset it would be called the greatest eastern elongation.
Mercury reaches its greatest western elongation on November 25, however the dates preceding and following this date are also good times to watch because Mercury will still be a good distance from the Sun and away from its glaring light. Mercury will rise in the east southeast about an hour before sunrise. At its brightest, Mercury shines at approximately -0.5 magnitude. Mars, which lies between Mecury and the rising Sun, is much more dim at the moment with a magnitude 1.5. Jupiter is brighter with a -1.5 magnitude, however it rises with the Sun and probably won't be visible until December when it begins to pull away from the Sun.
Mercury can be found in the constellation Libra. However, Libra is a rather unremarkable constellation. Mercury will simply be the brightest starlike object in the southeast just before sunrise. Mercury is actually a better marker for finding the constellation Libra than vice versa.
A special treat occurs on December 3 when the Moon occults the Pleiades. Start watching after sunset on December 3 as the Moon sneaks up on the stars in the Pleiades. Within a couple hours the Moon will begin to cross over the Seven Sisters. You can watch the stars wink out as they disappear behind the Moon's limb and then reappear minutes later. The bright Moon will be nearly full at more than 98 percent lit. Astrophotographers can get great photographs of the Pleiades playing hide and seek behind the Moon.
