September 2001

By Steve Stefanik

Sagittarius the hunter, the "last in line" of the summertime constellations, is due south after the sun sets as September begins. Its familiar "teapot" asterism, which is the heart of the Milky Way, plays host to the waning planet Mars. Mars will diminish both in size and brightness throughout the month from magnitude -0.9 and 13 arc seconds in apparent diameter to –0.4 magnitude and only 11 arc seconds across so this will probably be the last month to see any of its surface detail through a telescope. For those of you with binoculars or a telescope, you will be able to spot Mars within 2.5 degrees of M8, the spectacular "Lagoon Nebula" from September 8^th through the 10^th.

Another sign that summer is nearing its end and fall is not far away is the passing of the "Summer Triangle" west of our meridian, which consists of the three bright stars, Vega in the constellation Lyra, Altair in the constellation Aquilla, and Deneb in the constellation of Cygnus. Officially fall begins at 7:04 p.m. EDT on September 22^nd when the celestial equator (earth’s equator projected out into space) crosses the ecliptic (the imaginary path of the planets) due to its tilt with respect to the sun, which results in equal hours of daylight and darkness. The good news is that we will be able to observe the night sky earlier and longer.

If you go outside to view the late summer splendors of the night sky, look toward the western horizon about 30 minutes after sunset and try to spot the elusive planet Mercury. Look for it near the brightest star in the constellation Virgo, Spica. It will be slightly brighter and considerably redder in color than the blue star. Mercury will be at its highest above the western horizon when it reaches greatest elongation from the sun on the 18^th.

The planets Neptune and Uranus will be well placed for viewing this month. Both planets are in the constellation Capricorn the sea-goat, east of Sagittarius. You’ll need at least binoculars to spot these 5.7 and 7.9 magnitude planets respectively.

You’ll have to wait until after midnight to see the next planets rise above the eastern horizon.

The first to rise is Saturn. Look for the familiar rings of this 0.2 magnitude planet among the stars of the constellation Taurus the bull.

The planet Jupiter rises about two hours after midnight in the northeast in the constellation Gemini. You shouldn’t have a problem spotting this magnitude –2.1 giant with just your eyes.

The last planet to come into view is Venus. It rises between 4 and 5 o’clock in the morning just before dawn. It’s unmistakable –3.8 magnitude brilliance cannot be confused with anything else. It crosses the constellations Cancer the crab and Leo the lion during the month of September.