The planets Mercury and Venus will put on a good show for skywatchers throughout April, according to the editors of StarDate magazine. Mercury usually is difficult to see because it seldom moves far from the Sun, but April offers a good view of Mercury because the planet is farthest from the Sun for its current evening appearance and because it appears close to Venus.

Look for Mercury low in the west at sunset. It looks like a bright star. Much brighter Venus, the "evening star," helps point the way.

The crescent Moon joins these two planets on April 15 and 16. Mercury is just below the Moon on the 15th, and to its lower right on the 16th. The Pleiades star cluster, which marks the shoulder of Taurus, the bull, rounds out the view. It stands above the Moon on the 16th.

Because Mercury is always so close to the Sun, it is a difficult world to study. Most research telescopes can't aim close to the Sun because sunlight would overpower their electronic instruments.

And even when Mercury is far enough from the Sun to observe with a telescope, the planet is so low in the sky that the view is distorted because Mercury's light must travel through a thicker layer of Earth's atmosphere.

By far the best view of Mercury comes from spacecraft. Mariner 10 flew by Mercury three times in the 1970s and MESSENGER has made three passes in the last two years.

MESSENGER will enter orbit around Mercury next year, providing continuous coverage of the close but hard-to-study planet.