SKYLIGHTS
Astronomy news for the week starting Friday, June 30, 2000.
Nothing much happens today, Friday the 30th, but the next,
Saturday, July 1, is quite special. First, the Moon passes its new
phase and eclipses the Sun, but only partially and only in and
around one of the most inaccessible and dangerous places (for
sailors) on Earth, near Cape Horn, which lies at the southern tip
of South America. Second, on the same day, the Moon will also be
at perigee, when it is closest to the Earth. Since tides are very
sensitive to the lunar distance, the close coincidence will produce
very high and low water marks on the coasts. Third, in another
inaccessible event, Mars is in conjunction with the Sun. It will
now become visible in the morning sky, but because the planet moves
only slightly slower than the Earth, not until late July or early
August will it be visible in eastern morning twilight. Following
new, the Moon will pass through its crescent phase, and will become
barely visible in western twilight the night of Saturday, July 2.
Not to be outdone, Mercury passes inferior conjunction with the Sun
(when it is between us and the Sun) on Thursday, July 6. Since
Venus has just passed superior conjunction (when it is on the other
side of the Sun), it is invisible as well. If you want planets,
rise early to look at Jupiter and Saturn, which are now just
clearing morning dawn.
But it is Earth that makes the biggest splash, as it passes its
aphelion point, where it is farthest from the Sun, on Monday July
3, when it will be 152,102,000 kilometers (94,512,000 miles) from
the Sun. Rather obviously, since greatest distance coincides with
northern summer heat, the distance between Earth and Sun has little
to do with the seasons. Technically, on a world basis, aphelion
takes place in Greenwich Time at midnight beginning the 4th of July
(Happy Birthday).
As the sky darkens, look to the south to see Corona Borealis, the
Northern Crown, high and nearly overhead for most people in the US
(with apologies to Australians, who see it very low). Dim Libra is
down toward the horizon. If you are far enough south, look to the
west of Scorpius for the brilliant stars of Lupus, the Wolf, and
Centaurus, the Centaur (lucky Australians!). Even from the lower
US, you can see a fuzzy spot in the middle of Centaurus, southwest
of Antares in Scorpius. It is the greatest of globular clusters,
Omega Centauri, a huge cluster of a million stars easily visible to
the naked eye even though 17,000 light years away.
