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Starstruck

This Week's Night Sky: Spy Saturn’s Icy Moon Dione

Look for Venus as a "morning star," the moon with a stellar teapot, and—if you're more ambitious—a glimpse of Pluto this week.

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As it flew past one last time on August 17, NASA’s Cassini spacecraft captured this close-up view of Saturn’s icy moon Dione. This week, backyard astronomers can use small telescopes to glimpse Dione for themselves.


Pluto Views.  We got an amazing view of the dwarf planet in July when NASA’s New Horizons spacecraft flew by, and sky-watchers can still get a good glimpse of this distant world through backyard telescopes this week.

Late night on Monday, look for Pluto nestled with the southern constellation Sagittarius, which is now visible late nights in the southern horizon for those in the mid-northern latitudes.

But be aware that Pluto remains a difficult observing challenge. Lying 3 billion miles (4.9 billion kilometers) from Earth at the fringes of the solar system, it shines at a meager 14.1 magnitude and looks like a faint star. That means backyard sky-watchers need, at a minimum, a telescope with an 8-inch diameter mirror to glimpse the faint world.

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The giant stellar teapot formation in the constellation Sagittarius can be spotted easily on August 25, thanks to the moon perched right above it.


Check out the Sky and Telescope website for a detailed finder chart that will help you pick Pluto out from the surrounding star field.

And when you see a speck, just remember that the wonderment lies in simply tracking down this distant icy world and seeing it with your own eyes.

Moon meets Teapot.  On Tuesday evening, look for the waxing gibbous moon to pose with the great celestial teapot star pattern in the constellation Sagittarius, now visible in the low southern sky.

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Look for bright yellow-colored Saturn in the southern sky in the late evening. The inset shows the high-magnification view through a telescope, and the location of Saturn's moons, including Dione, on August 29.


Dione Views.  After darkness falls on Saturday, check out Saturn’s moon Dione, which was just barnstormed by NASA’s Cassini spacecraft last week.  

Dione measures only 683 miles (1,120 kilometers) across and orbits 235,000 miles (378,000 kilometers) from Saturn, taking 2.74 days to orbit the gas giant.

Tonight, the fourth largest moon of Saturn will be visible through a small backyard telescope under high magnification, right next to its fellow moons Tethys and Rhea.

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This skychart show Venus and Mars posing in the low eastern horizon 30 minutes before local sunrise on August 30.


Dione is thought to have a rocky core but is covered with highly reflective water ice. The Voyager and Cassini missions have shown close-up views of its complex surface, revealing giant sets of fractures, impact craters and cliffs.

Morning Star.  About a half-hour before local sunrise on Sunday, look toward the very low eastern horizon for the bright star-like Venus. After weeks of hiding within the glare of the sun, the planet returns to the morning skies. Joining it is the ruddy planet Mars, located to Venus' upper left.  

While Venus is a fairly easy target to pick out from the glare of the sunrise, fainter Mars will be a bit more challenging and requires binoculars to hunt down. But once you know where to look for the Red Planet, see if you can spot it with just your unaided eyes.

Clear skies!

Follow Andrew Fazekas, the Night Sky Guy, on Twitter, Facebook, and his website.

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