Mercury set to exit dance of planets

(CNN) -- The closest planet to the sun will soon fade from sight, but celestial watchers still have time to spot it along with all the other four naked-eye planets in a rare twilight display.

For weeks to come, Mercury, Venus, Mars, Jupiter and Saturn will keep together in close formation shortly after sunset in Western skies.

But during that time, the first planet will gradually drop from the dance, hidden by the glare of the sun, while the latter four continue moving around each other into the summer.

The dancing planets form picturesque displays. On Monday, Mars, Saturn and Venus made a close-knit triangle. On Friday, Venus and Mars will hover within one-third of a degree of each other. To compare, the tip of a finger extended at arm's length is two times as wide.

Perhaps the most anticipated show comes May 14 and includes an entirely different performer. Venus will pass within a fraction of a degree of the moon. At the time the moon will appear as a slender crescent, but the dark portion will glow with "earthshine," or sunlight reflected off our planet.

The Venus-Moon duet is "a sight you will never forget," wrote Jack Horkheimer, director of the Miami Planetarium, on his Web site: http://www.jackstargazer.com

"If you have any way of photographing this event please do so because it's simply the kind of celestial picture that will take your breath away."

A close line-up of the five naked-eye planets like this one happens only once every generation or so. A similar planetary grouping will not take place until 2040, according to Kelly Beatty, executive editor of Sky & Telescope Magazine.

To view the show, Beatty suggests looking in the direction of where the sun sets about 45 minutes later. To see Mercury, which hangs extremely low in the sky, a clear view to the Western horizon is necessary. Binoculars can help to compensate for sun glare.