SKYLIGHTS
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.
