SKYLIGHTS

Astronomy news for the week starting Friday, May 25, 2001.

The Moon passes through its first quarter this week on Tuesday, May 29. The night of Friday, the 25th, the slim crescent will (for those in the Americas) stand smack in the middle of Gemini with Castor and Pollux right above it as it sets. Two days before the quarter, the Moon passes its perigee point, where it is closest to the Earth.

The dark markings on the lunar surface, the "maria," or "lunar seas," are huge lava-filled impact basins -- just very large craters. Three of these circular features are readily visible at first quarter. From upper left to lower right, see if you can make out Mare Serenitatis (the "Sea of Serenity"), Mare Tranquillitatis (the "Sea of Tranquillity"), and Mare Foecunditatis (the "Sea of Fertility"). Toward the right edge of the Moon perhaps you can also make out smaller Mare Crisium (the "Sea of Crises"). Apollo 11, carrying the first lunar voyagers, set down on Mare Tranquillitatis on July 20, 1969.

Saturn is truly gone from sight as it passes conjunction with the Sun this week, on Friday, the 25th. You can forget Jupiter too, at least for now. Both planets, however, will make nice display pieces in the morning sky by mid-summer. By odd coincidence (such abound in astronomy, as there are so many events going on), the planet Uranus enters retrograde motion in eastern Capricornus at almost exactly the moment that the Moon passes first quarter. At bright sixth magnitude, Uranus is just visible to the naked eye in a dark site with no moonlight present. Neptune (a telescopic planet), to the west of Uranus, began its retrograde movement earlier in the month. Mars is moving backwards too, though since it has just reversed its direction at a not-very-fast pace. That will pick up as the red planet approaches its very bright opposition to the Sun on June 13. By then it will have moved from its current residence in Sagittarius into Ophiuchus, the only constellation not of the classical zodiac through which runs the ecliptic (the apparent path of the Sun).

If you are far enough south, this is the moment for the Southern Cross, which crosses the meridian in early evening around the time that northern observers see Corvus the Crow to the exact south. In between is the tail of Hydra, the Water Serpent, and the bright stars of western Centaurus. The top two stars of Corvus point leftward to Spica, in Virgo. If decently south of 40 degrees north latitude, look about 35 degrees due south of Spica to see the fuzzy ball made by the greatest star cluster in the Galaxy, the magnificent globular cluster Omega Centauri.