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AURORA WATCH: Although solar activity has been mostly low this week, auroras are possible tonight at high latitudes--e.g., Scandinavia, Alaska and Canada. The cause: high-speed solar winds blowing past Earth. NOAA forecasters estimate a 10% chance of severe geomagnetic storms. [gallery]
EARTHSHINE: Step outside tonight around sunset and look west. There's a beautifully slender crescent moon near the horizon; you can see it even before the sky fades completely black. Can you also see a ghostly glow across the moon's dark terrain? That's Earthshine--one of the prettiest sights in the heavens. [sky map]
Right: A crescent moon with Earthshine, photographed by Gary Syrba of Grand Rapids, Michigan, on Sept. 12th.
URANUS: Earth and Uranus are having a close encounter this month; the two worlds are "only" 2.9 billion km apart. Shining like a 6th magnitude star, Uranus is barely visible to the unaided eye. Look for it in the constellation Aquarius around 10 o'clock at night, but don't bother unless you have very dark skies. [sky map]
Better yet, use a telescope. Ralf Vandebergh of the Netherlands took the above picture of Uranus on Sept. 16th using a 10-inch telescope and a digital web camera.
"Uranus has a strong polar flattening due to its fast rotation (17 hours and 14 minutes)," says Vandebergh. "This image clearly shows the flattening. It was also observable by eye--simply looking through the telescope's eyepiece--at 300x in excellent seeing."
SUNSPOT EVOLUTION: Sunspots aren't static; some of them evolve rather quickly. Witness this three-day animation of sunspot 672 spanning Sept. 14th - 16th:
The group's leading spot, about the size of planet Earth, splits into several pieces while other members fade completely. Unseen magnetic fields above the active region are changing, too, twisting, turning, poised to snap--this is how solar flares erupt. But, in this case, solar flares are unlikely. The sunspot is rapidly dissolving and poses a declining threat for major eruptions.