The moon meets the Pleiades in April

March 31, 2008

Saturn. Photo by: NASA

The Pleiades star cluster will have a beautiful encounter with the slender moon in the western sky after sunset on April 8. Usually the moon's brightness overpowers nearby stars, but not when it's such a thin crescent. Binoculars will reveal the spectacle as the moon passes just below the famous Seven Sisters.

The Pleiades (pronounced PLEE-ah-deez) are lovely by themselves, and on a clear night they can be seen with the unaided eye in the constellation Taurus the Bull. Known prehistorically, the 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 http://antwrp.gsfc.nasa.gov/apod/ap021201.html and other Web sites as well.

Saturn will be high in the southeast as darkness falls on April evenings, one of the first "stars" to appear and a fine sight in any telescope. It will be visible much of the night in the constellation Leo the Lion, near Leo's brightest star, Regulus. Saturn's rings will open slightly during April, but they will be nearly edge-on and invisible to us by the end of the year. Titan, Saturn's largest moon, will be due south of the planet on April 2 and 18 and due north on April 10 and 26.

Jupiter will rise around 3 a.m. local daylight time at the beginning of April and two hours earlier by month's end. Wait until the brilliant white object is high in the southern sky and then use binoculars to see its four largest moons, which Galileo discovered with one of the first telescopes. These tiny bits of white light are strung out in a straight line on both sides of Jupiter, and they seem to slide back and forth along the line from one night to the next as they orbit the planet. You may need to steady your binoculars by resting your elbows on a surface to keep the image from wobbling. The only times you won't see all four moons are when one or more are crossing in front of the planet or behind it.

Mars will be conspicuous during April, glowing bright orange high in the west after dark as it passes through the stars of the constellation Gemini the Twins. This will be a good chance to compare the similar colors of Mars and the bright star Pollux as they draw closer. Binoculars will make the colors stand out.

Mercury will be lost in the sun's glare during most of April for observers in the Northern Hemisphere. By month's end, it will appear below the Pleiades star cluster low in the west-northwest half an hour after sunset. Those in the Southern Hemisphere will be able to see the small planet in early morning twilight for the first half of the month.

Starting in April, Venus will be hidden in the glare of the sun for an unusually long time for observers in the Northern Hemisphere. The brilliant planet will be on the far side of the sun from us as it moves from morning to evening twilight. Not until July will Venus again be visible near the western horizon. Seen from the Southern Hemisphere, Venus will rise 90 minutes before the sun and be conspicuous in the morning sky.

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 is encouraging people in the United States to turn off unnecessary outside lighting during National Dark-Sky Week, which lasts until April 4. More information is available at http://www.ndsw.org .

Meteor shower

The Lyrid meteor shower will peak on the night of April 21-22. About 20 Lyrids per hour are normally visible after midnight, but this year the full moon's glare will hide the fainter ones. To minimize this effect, try watching from a place where the moon is blocked by a building or trees. 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, beginning around midnight local time in the Northern Hemisphere and lasting the rest of the night. The later the hour, the more meteors there will be.

Summer Triangle

Spring weather can be fickle, but a reliable sign that the seasons are changing is the appearance of a trio of bright white stars called the Summer Triangle. Vega will be the first to rise each night in the east, leading the way high across the sky. The other stars are Altair in the constellation Aquila the Eagle to the south and Deneb in the constellation Cygnus the Swan to the north. When you are looking from Deneb to Altair, you are also looking at the Milky Way, though it's usually obscured by city lights. If you find a place dark enough for you to see the Milky Way, keep the location in mind -- you'll also see a lot more meteors and other celestial objects from there. A photograph of the Summer Triangle is at http://www.allthesky.com/various/sumtri.html. Click on the photo to enlarge it. If you have trouble picking out the three brightest stars, click on "labels on/off" to identify them.

Moon phases

The moon will be new on April 5, at first quarter on April 12, full on April 20 and at third quarter on April 28.

Source: Indiana University