SKYLIGHTS

Astronomy news for the week starting Friday, May 11, 2001.

The Moon fades the beginning of the week through its gibbous phase, passing third quarter on Tuesday, the 15th (about the time it crosses the meridian to the south for those in North America), thereafter waning through crescent. Just two hours before the quarter, the Moon will pass three degrees south of Uranus (which recently passed into extreme southwestern Aquarius), and only nine hours before the quarter it passes through its apogee, when it is farthest from Earth, 404,000 kilometers, or 251,000 miles. At that time, the Moon will be about as small in angle as possible, though without comparison, the effect is not visible to the eye. Ocean tides, however, with solar tides pulling against lunar, and with the Moon at maximum distance, will be distinctly minimized.

The sky belongs to the planets that bracket the Sun. Showy Venus, still near its greatest brilliance, dominates the morning dawn sky, and now rises almost exactly as astronomical twilight (which starts when the Sun is 18 degrees below the horizon) begins. Rapidly encroaching on the evening sky is Mars, which rises in the southwest about 11 PM daylight time. The Earth has now caught up with the red planet to the point that Mars begins its retrograde motion on Friday, May 11th. At that moment, it stops its usual westerly movement (now among the stars of Sagittarius), and starts to go backwards, to the west, as the Earth prepares to swing between it and the Sun. Neptune, in Capricornus, enters retrograde the day before.

Other planets are not to be discounted, however. Jupiter is still visible in the west in evening twilight, and Mercury begins to make an appearance as well. As the week begins, look for the little planet down and to the right of Jupiter, the giant planet notably the brighter. By Wednesday, the 16th, Mercury will have moved three degrees (six times the angular diameter of the Moon) directly north of Jupiter.

As the Earth turns around the Sun, the stars of a given hour move slowly westward. At 9 PM daylight time, the bowl of the Big Dipper is high to the north for most in North America. If far enough south, below 25 degrees north latitude, you can admire the Southern Cross, which lies directly south of the Dipper's handle. If you cannot see the Southern Cross, however, you certainly can appreciate the Northern Cross. This large figure, Cygnus the Swan seen upside down, can be found climbing the northeastern sky after midnight. In between the Dipper and the Southern Cross, to the south in mid-evening, lie Leo and Virgo, and below them one of the faintest of all classical constellations, Crater, the Cup, which sits upon eastern Hydra, the Water Serpent.