Late April

As the planets align, Mercury dances in and out of the show. To spot it, you'll need to act quickly.

In the third week of April, Mercury peeks above the horizon to join the other bright planets. Use this map to find them.

This will be Mercury’s best apparition of 2002. It began April hiding behind the Sun’s glare and coming to superior conjunction -- located on the opposite side of the Sun as viewed from Earth -- back on April 7. But then, in its small orbit, it quickly rounded the Sun and will soon climb into view above the west-northwest horizon.

Using binoculars, watch Mercury pass just over 1½ degrees south of the Pleiades star cluster on April 29. Actually, it should be at its most prominent before the end of the month, because it will be fading rapidly as it appears in telescopes to wane from a gibbous to a crescent phase (like the Moon, Mercury is illuminated in phases as seen from Earth). By the April 30, Mercury is only about one-third as bright as it will be on the 22^nd.

The planet alignment will culminate in early May with Venus, Saturn and Mars squeezing into an unusually tight and very eye-catching triangle configuration.

Editor's Note: Return May 3 for another viewer's guide to the developing planet alignment. Also, on April 30, SPACE.com columnist Joe Rao will lecture on the upcoming planet alignment. The lecture is part of the monthly Celestial Highlights program at the Hayden Planetarium in New York City. More information is available here.

Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.