Most people have never knowingly seen Mercury. That's a pity, because viewing the innermost planet is very rewarding, whether you use a telescope, binoculars, or just your unaided eyes.The problem with Mercury is that it never strays far in the sky from the Sun, so it's usually visible only very close to the horizon in bright twilight. But people at mid-northern latitudes (the US and most of Canada, Europe, and Asia) have an extraordinarily good opportunity to view the elusive planet on evenings in May 2008. Throughout most of the month, Mercury is high above the western horizon a half hour after sunset, and it's still reasonably high even an hour after sunset, when the Sun's glow is quite subdued.
As always when it's visible in the evening, Mercury is brightest at the beginning of the apparition, fading from magnitude -0.8 on May 1st to 0.3 on May 12th. That's nearly a threefold decrease, but magnitude 0.3 is still dazzlingly bright.
Mercury fades rapidly after mid-month, making it a challenging target for the unaided eye. But this is also when the planet is at its best through a telescope, swelling in apparent diameter and thinning to a crescent as it starts to come between Earth and the Sun. Following Mercury with a telescope throughout an entire apparition is surprisingly satisfying.Mercury makes interesting patterns with other astronomical objects on two occasions in May. From May 13, it passes just to the left of the Pleiades. The planet will be easy to see, but you might need binoculars to spot the Pleiades when they're so low in the sky. In any case, the cluster and the planet will fit easily in a single binocular field of view.
Then on Tuesday, May 6th, North Americans can watch Mercury make a spectacular pairing with a 1½-day-old crescent Moon. It's almost identical to the scene shown at right, except that the positions of the bodies will be reversed, with Mercury to the Moon's lower left.