SKYLIGHTS
Astronomy news for the week starting Friday, July 30, 1999.
The Moon wanes through its gibbous phase the first part of the
week, passing third quarter on Wednesday, August 4th, thereafter
beginning to fall through crescent toward new on the 11th, at which
point it will eclipse the Sun, the event to be seen through Europe.
The day before, the night of Tuesday, the 3rd, the Moon will pass
a few degrees south of bright Jupiter, now rising ever earlier in
southwestern Aries. The night of the last quarter, the 4th, the
Moon will then pass about the same distance south of Saturn, the
two giants of the Solar System drawing ever closer as seen from
Earth.
Venus is now effectively gone from the evening sky. Though still
to the east of the Sun, Venus is setting in twilight that is so
bright that the planet is very hard to see. That leaves the
evening sky to reddish Mars, which is moving to the east against
the stars of Libra and is now about half way between Spica in Virgo
and Antares in Scorpius. Of course you might also count little
Pluto. Though you cannot see it without a fairly large telescope,
you can still appreciate its position up and to the left of Mars
and 16 degrees due north of the bright star Antares in Scorpius.
The dimming Moon brings out the stars once again. High overhead in
mid evening lies brilliant Vega, shining at magnitude zero. To the
east of it is the prominent figure of Hercules, the northern four
stars making a box called "the Keystone." At the northwestern
corner of the Keystone is a small fuzzy patch barely visible to the
naked eye but quite obvious in binoculars. A telescope reveals it
to be a magnificent "globular cluster" that contains roughly a
million stars packed into a volume no more than 100 light years
across. Known as Messier 13, it is a classic celestial showpiece.
Open clusters like winter's Pleiades abound in our Galaxy, but only
about 150 globulars are known. If you look directly to the right
of Antares in Scorpius you can find another, Messier 4, and yet
another, Messier 22, is easily found just to the north of the
single-star handle of the Little Milk Dipper in Sagittarius. Stars
are so densely packed at the centers of these systems that they
actually collide with each other. Globular clusters lie in an
extended halo that surrounds the disk of the Milky Way; as the
oldest members of our Galaxy, formed some 12 to 14 billion years
ago, they tell us that the halo came first.
