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University of Minnesota

Starwatch September 2012

August 17, 2012

Eagle Nebula.

The "Pillars of Creation" are stellar nurseries in the Eagle Nebula, made famous by this iconic image from the Hubble Space Telescope.

By Deane Morrison

As September turns summer into fall, our old friend Saturn sinks into the sun's afterglow. Left behind—for now—in the evening sky, Mars manages to avoid the same fate.

But Mars is fading as it falls ever farther behind Earth in the orbital race. If you have trouble finding it above the western horizon, on the 19th a waxing crescent moon hovers just to the left of the planet.

It is, of course, considerably easier to find the Mars in the news, thanks to NASA's Mars Science Laboratory (Curiosity) mission team, who pulled off an incredible feat by landing the big rover on target. Curiosity will explore about a billion years' worth of rock strata in Mars' Gale Crater, looking for signs that the planet once could have harbored life.

Early risers will see a last-quarter moon glide close to Jupiter, in Taurus, the morning of the 8th, and on the 12th a waning crescent appears next to brilliant Venus in the predawn hours. On the 13th and 14th, Venus passes south of the faint but lovely Beehive star cluster.

In September the Summer Triangle of Vega (west), Deneb (east), and Altair (south) reaches its highest point in the south. So does Capricornus, the sea goat, a faint, chevron-shaped constellation south and slightly east of the Triangle.

Look just northeast of Altair to see little Delphinus, the dolphin, leaping above the sea that is the Milky Way. And northwest of Altair, about a third of the way to Vega, binoculars and dark skies may help you find the Coathanger of stars hanging almost upside down.

The autumnal equinox ushers in fall at 9:49 a.m. on the 22nd. At that moment the sun will be directly above the equator and Earth will be lighted from pole to pole.

The equinox is also a time of change. Since the summer solstice, the sites enjoying "midnight sun" have been retreating northward. At fall's arrival, the sun officially sets at the North Pole, extinguishing the last rays of midnight sun in the Northern Hemisphere for six months.

Also, the last six months have been a time when the farther north you went, the longer the daylight hours you enjoyed. At the fall equinox, however, this pattern reverses, and it's the travelers going south who will see more daylight.

The full harvest moon shines the night of the 29th. This moon has long helped farmers working late to harvest crops because around the time of fullness it rises as little as 20-25 minutes later from night to night.

This phenomenon stems from the fact that full moons are opposite the sun in the sky. Therefore, when the sun is heading south most rapidly—as it is around this equinox—the fullish moon is climbing northward most rapidly from night to night and so rises only a little later each time. At the spring equinox, we see the opposite effect: a near-full moon that rises some 75 minutes later on subsequent nights.

The University of Minnesota offers public viewings of the night sky at its Duluth and Twin Cities campuses. For more information and viewing schedules, see:

Duluth, Marshall W. Alworth Planetarium:

Twin Cities, Minnesota Institute for Astrophysics (during fall and spring semesters):

Check out the astronomy programs at the University of Minnesota's Bell Museum ExploraDome:

8/20/12 Contact: Deane Morrison, University Relations, (612) 624-2346,

Find U of M astronomers and links to the world of astronomy at

Tags: College of Science and Engineering

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