SKYWATCH

July 1995

by Steve Stefanik

Now that summer has officially arrived, the days are longer and the nights are shorter. All one has to do is look to the east in the late evening to see the familiar "summer triangle" stars of Vega, Deneb, and Altair. Vega, in the constellation Libra, is the brightest star (zero magnitude) in the northern hemisphere now that Sirius (magnitude -1.0) has set in the west. Altair, in the constellation Aquilla the eagle, is the second brightest (first magnitude) star of the asterism. Deneb, also a first magnitude star, marks the head of Cygnus the swan in the great northern cross.

Mars is still the first planet visible in the southwest as the sun sets. Although it is only a fraction of the brightness it was this past winter, it can still be seen with the naked eye lower and to the left of the constellation Leo. It will enter Virgo by mid-July.

The brilliant object (magnitude -2.4) you see in the south this July is the Jovian giant planet Jupiter. It is well placed in the easily recognizable constellation of Scorpio. Look for it above the stars that form a huge "J". The bright red first magnitude star below it is Antares.

The constellation that follows Scorpio to the east is Sagittarius the archer which looks more like a teapot than a bow and arrow. When you look in this part of the sky you are looking inward toward the center of the galaxy. Some of the "stars" you see in this region are actually globular clusters which through a telescope you would actually see are tightly grouped clusters of stars themselves.

Also located among the stars of Sagittarius are the two planets Uranus and Neptune. Both reach opposition (directly opposite us from the sun) this month so they are at their brightest. Uranus, the closer of the pair, reaches a naked eye magnitude of +5.6 on the 17th and Neptune will become a +7.9 magnitude "star" on the 21st. Try locating the two through binoculars. They will appear blue-green in color.

Saturn rises before mid-night by month's end in the east-southeast below the great square of Pegasus, the mythological flying horse. This is the year that it's all too familiar rings have disappeared. It will look like Jupiter through a telescope. You may even see some of it's moons pass in front of the planet or disappear behind it.

The only other planets to be seen are Mercury and Venus but you'll have to be up 30 minutes before the sun rises and look low along the eastern horizon to catch a glimpse of the pair. Venus is the brighter of the two at a blazing -3.9 magntude. Mercury is merely a +0.2 yellow-orange dwarf by comparison.