July 2002

By Steve Stefanik

July is the month that a giant "J" of stars stands prominently above the southern horizon in late evening. This is the summer constellation Scorpio, the mythological scorpion. The bright red first magnitude star, Antares, depicts its "head". Literally translated it’s name means "rivaling Mars" which is in reference to the similarity in color (red) and brightness (when Mars is at opposition).

July is also the month that the brightest star in the constellation Canis Major (the big dog) and in the entire sky, Sirius, is in conjunction with the sun. In ancient times it was commonly believed that the heat from the combined pair gave rise to the extreme heat of summer, which became known as "the dog days of summer".

The only planet that can be seen easily in July’s late evenings is Venus. If you look in the western sky about 45 minutes after sundown you are sure to spot this unmistakable –4.0 magnitude beacon about 15 degrees above the western horizon. It sets about 2 hours after the sun.

There are other planets that can still be seen however. If you scan the northwestern horizon with binoculars about half an hour after the sun goes down you may be able to spot –1.8 magnitude Jupiter and +1.8 magnitude Mars about 1 degree to the upper right of Jupiter. You’ll have to hurry though because they set within and hour of the sun.

About the time Venus sets two more planets will rise in the east, Neptune and Uranus, but you’ll need binoculars or a small telescope to spot them. Neptune is the first to rise among the stars of Capricorn. At +7.9 magnitude it’s a tough target even with binoculars. Uranus rises about an hour later in the constellation Aquarius. It is almost 2 magnitudes brighter than Neptune at +5.8 magnitude and much easier to spot in binoculars.

The remaining two planets visible this month are Saturn and Mercury but you’ll have to be up before dawn to view them. Saturn reappears in the eastern predawn sky amid the stars of the constellation Taurus the bull, where it was when it set in the west after May’s spectacular conjunction of 5 planets. The planet Mercury hovers very close to Saturn in the beginning July. It is the brighter of the pair at –0.3 magnitude and continues brighten to –2.1 magnitude the first 3 weeks of the month. Saturn is considerably dimmer at +0.1 magnitude. Viewing the "ringed planet" will be much easier next month.