STAR TRAK for April: Mercury makes best evening appearance

(PhysOrg.com) -- For observers at mid-northern latitudes, Mercury will make its best evening appearance of the year during the first half of April. During those two weeks, the elusive planet will be at least 10 degrees above the west-northwestern horizon a half-hour after sunset, lingering there until the end of twilight. It will fade considerably during that period, however, so binoculars may be needed to see it by midmonth. On April 8, Mercury will reach its greatest elongation from the sun.

As you wait for Mercury to appear, you can watch Venus gleam dazzlingly bright low in the west. Venus will be a helpful marker in finding Mercury, for the two planets will be about 3 degrees apart at the beginning of the month. For the first week, they will keep about the same separation from each other as they move upward. After April 8, however, fading Mercury will drop back toward the sun while Venus maintains its brilliance as it continues to climb higher in the darkening sky.

A few degrees above Venus will be a lovely cluster of stars called the Pleiades (pronounced PLEE-ah-deez). On a clear night they can be seen with the unaided eye low in the west, and binoculars will give an even better view. Known prehistorically, this cluster is identified as a group of women in many cultures around the world, from Australian Aborigine to Native American. A photograph of the Pleiades can be seen at antwrp.gsfc.nasa.gov/apod/ap021201.html and other Web sites as well.

The best time to view Mars during April will be when it is high in the southwest shortly after dark. The orange planet will remain visible until well past midnight. From April 16 to April 18, Mars will pass just north of the Beehive star cluster, offering a pretty sight in telescopes and binoculars.

Saturn will be well above the southeastern horizon as darkness falls on April evenings, one of the first "stars" to appear. Saturn passed closest to Earth last month, so it will remain near its peak of visibility for most of the night throughout April. The best views through a telescope will be when it is high in the sky around local midnight. Bright yellow Saturn will outshine nearby Spica, the brightest star in the constellation Virgo the Maiden. See saturn.jpl.nasa.gov/home/index.cfm for the latest news and images from the Cassini spacecraft orbiting Saturn.

Jupiter will rise shortly before the sun during April, but it will be bright enough to spot easily low in the east-southeast at dawn.

Light pollution

A great deal of energy and money is wasted on inefficient, improperly directed outdoor lighting. To help call attention to this problem of light pollution, the International Dark-Sky Association encourages people in the United States to turn off unnecessary outside lighting during National Dark-Sky Week. This year NDSW will be from April 4 to April 10. More information is available at www.darksky.org/ .

Meteor shower

The Lyrid meteor shower will peak during the hours before dawn on April 22. For observers in North America, 15 to 25 meteors per hour should be visible in a clear, dark sky after the moon sets around 3 a.m. local time. The meteors can appear anywhere in the sky, but they will seem to come from a point called the radiant in the constellation Lyra the Harp, which gives the shower its name. Lyra's bright white star Vega will be almost at the radiant, and the meteor count should be highest when Vega is well above the eastern horizon. The later the hour, the more meteors there will be.

Moon phases

The moon will be at third quarter on April 6, new on April 14, at first quarter on April 21 and full on April 28.