Astronomy news for the week starting Saturday, March 25, 2000.

Skylights will now resume its normal Friday schedule. The Moon begins the week in its waning gibbous phase, passes third quarter the evening of Monday the 27th, and rises that night in North America just a bit past the quarter as it enters its waning crescent phase. Just seven hours before the quarter, the Moon passes apogee, the point where it is farthest from the Earth (typically 5.5 percent farther than average). On Thursday, the 30th, the Moon will pass and actually (if you happen to live in Antarctica) cross over Neptune.

The combination of quarter Moon and apogee will make for especially small ocean tides. A tide is a stretching force caused by the difference in solar and lunar gravity across our planet, and is most obvious in ocean waters. At the quarters, the tide from the Sun acts in the perpendicular direction relative to that from the Moon, and the weaker solar tide partially fills in the lunar tide. The strength of a tide is also very sensitive to the distance between the Earth and the Sun or Moon, and with the Moon 5.5% farther than average, the lunar tide weakens by some 17%. The early evening sky is taking on a particularly lovely aspect as Jupiter and Saturn descend into the west. Jupiter, by far the brighter of the two, now sets around 9 PM. Saturn follows by half an hour as the two gradually draw together for their Grand Conjunction in the morning sky of May 31. At the same time, both are now encroaching on Mars, which lingers dimly and redly in the evening sky, now setting around 8:30 PM. The morning, however, is losing its glorious Venus, which is very difficult, if not impossible, to find in eastern twilight. Indeed, Mercury, which makes a brief morning appearance, is above it. The little planet reaches its greatest western elongation on Tuesday, the 28th (when it is as far to the west of the Sun as possible), but because of the low angle of the zodiac to the horizon, it will also be very hard to find.

Leo, that great signal of Spring, which is now upon us, roars high in the sky to the south at 11 PM. At the south end of the obvious Sickle that makes his head lies the first magnitude star Regulus. Below and to the right of Regulus is the "solitary one," Alphard, the luminary of Hydra, the Water Serpent. Due south of Regulus and just to the left of the line connecting Regulus and Alphard is the dim "modern" constellation Sextans, the Sextant, invented in the seventeenth century to honor the great invention that allowed for the measures of the stars in their places and for navigation across the waters and lands of the Earth.
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