Astronomy news for the week starting Friday, June 25, 1999.
The Moon heads toward its full phase this week, reaching it on
Monday, the 28th, shortly before moonrise in North America, making
the full Moon rise just a bit after sunset. Three days before, on
Friday the 25th, the Moon goes through its apogee, where it is
farthest from the Earth, a distance 5.5% greater than average.
Venus still dominates the evening sky to the west, while Mars, to
the south, comes in at close second place while it slowly pulls to
the east of the bright star Spica. Third and last in line among
evening planets is Mercury, which is making a fine appearance in
the northwest shortly after sundown, setting an hour and a half
after the Sun. On Monday the 28th, the little planet, the smallest
in the Solar System save Pluto, will reach greatest eastern
elongation, when it is a nice 26 degrees to the east of the Sun.
Though Mercury is very bright, at elongation comparable to Vega and
Arcturus (the latter high to the south as the sky grows dark), it
is hard to see against the twilight sky. A quick scan with
binoculars, however, will pick it up easily. If you wish to see
the other two planets, Jupiter and Saturn, you will need to stay up
until the morning hours past 2 AM to watch them rise in the east,
Jupiter first, the bright planet now gliding in direct motion to
the east against the stars of Pisces.
Since the near-full Moon will wash out all but the brighter stars,
it is a good time to admire the brightest the sky has to offer.
Vega, now climbing the northeastern sky in early evening is of
magnitude zero and just slightly less bright than Arcturus, the two
providing a fine color contrast, Vega white and Arcturus a soft
orange (different eyes seeing distinctly different shades).
Compare Arcturus with Antares in Scorpius low to the south around
11 PM, the supergiant Antares the cooler, and thus the redder, of
the two, its color enhanced by atmospheric absorption due to its
low altitude above the horizon. To the east again, Vega is the
northwestern apex of the rising Summer Triangle, which also
contains first magnitude white Deneb in Cygnus, east of Vega, and
also-white Altair in Aquila, which anchors the Triangle to the