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Hal Kibbey

Last modified: Friday, September 2, 2011


Sept. 2, 2011

BLOOMINGTON, Ind. -- Jupiter will be approaching opposition during September, when it will be opposite the sun in Earth's sky. This means that views of Jupiter through a telescope will be about as good as they can get.


Photo courtesy of NASA


Print-Quality Photo

At the start of the month Jupiter won't rise until about 10 p.m. EDT, but by month's end it will appear around the end of evening twilight and be high enough in the east by midnight for good telescopic viewing. For observers in the Northern Hemisphere the best images will come in the early morning hours, when the planet will be nearly overhead and its light will therefore pass through less of Earth's image-distorting atmosphere. With no bright stars nearby, Jupiter will be easy to spot.

Venus will emerge from behind the sun into the evening sky during September, but it will be too close to the sun for good viewing. At month's end it will be barely visible above the western horizon 25 minutes after sunset.

As the evening sky darkens early in the month, yellow Saturn will be visible very low in the west, with the bright white star Spica nearby on the left (south) at about the same elevation and brightness. Saturn will sink lower each day, and by mid month it will be too close to the sun to be seen.

Mars will rise in the east-southeast around 2 a.m. EDT throughout the month. On Sept. 15, the red-orange planet will form a straight line with the bright stars Castor and Pollux in the constellation Gemini the Twins. On the morning of Sept. 30, Mars will be about to enter the Beehive Star Cluster, a beautiful sight in binoculars.

Mercury will be visible very low in the east about a half hour before sunrise on Sept. 1. The white pinpoint of light will reach its greatest elevation on Sept. 3, when binoculars may show the bright white star Regulus in the constellation Leo the Lion about one field of view below Mercury. The planet will move even closer to Regulus over the next few days, and by Sept. 8 it will be just 1.3 degrees above the star, when the two will make a fine pair with either binoculars or the unaided eye. Mercury will be about eight times brighter than Regulus. During the following week they will drift apart as Mercury drops back toward the solar glare until it disappears from view. Mercury will pass behind the sun on Sept. 28.


On a clear September night you may be lucky enough to see an aurora (sometimes called "northern lights"). These silent ribbons and curtains of light can appear whenever the sun is active, but they are especially likely from August to October. Eruptions from the sun's surface hurl enormous amounts of charged particles into space, and when some of these solar particles head in our direction, they cause auroral activity. For details and photographs, see You can watch for auroras when they are most likely to happen by checking sites such as and Sightings of auroras are reported at


The sun will reach the September equinox on Sept. 23 at 5:05 a.m. EDT (9:05 Universal Time) marking the start of autumn in the Northern Hemisphere and spring in the Southern Hemisphere. For the next six months in the Northern Hemisphere, the nights will be longer than the days.

Moon phases

The moon will be at first quarter on Sept. 4, full on Sept. 12, at third quarter on Sept. 20 and new on Sept. 27.