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How to Spot Asteroid 2004 BL86, in the Sky and Online

A mountain-sized asteroid zoomed harmlessly past our planet on Monday, and it's not too late to see the space rock online or in the sky.

Radar readings show that the asteroid, known as 2004 BL86, is about two-tenths of a mile wide (300 meters wide), researchers at NASA's Jet Propulsion Laboratory said. They also reported that the asteroid appears to have boulders on its surface — and a tiny moon nearby.

Observers might be able to see 2004 BL86 with binoculars or a small telescope because of its significant size. At about 11 a.m. ET, the asteroid made its closest approach to Earth, coming within about 745,000 miles (1.2 million kilometers). NASA says the asteroid posed no danger to our planet.

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The Slooh virtual observatory presented a webcast about the asteroid via Slooh.com on Monday, featuring live commentary from Paul Chodas, a NASA expert on near-Earth objects, and NASA research scientist Lance Benner. [Photos: Potentially Dangerous Asteroids]

Benner showed off radar imagery of the space rock, captured overnight by the Goldstone radio telescope in California. "This is an object that's rounded," he said. "It has a moon."

Benner said the radar patterns also suggested there were boulders on the mountain-sized rock's surface. Additional imagery would be captured Monday night, he said.

At 2:30 p.m. ET, the Italy-based Virtual Telescope Project will offer a second webcast of the asteroid at http://www.virtualtelescope.eu/webtv/.

The asteroid is not visible to the naked eye, but it's definitely within reach to observers with binoculars or a 3- or 4-inch telescope who know when and where to look, according to a skywatching alert from Sky & Telescope magazine.

Image: Asteroid and moon
Radar readings from the Goldstone radio telescope in California show the rounded shape of asteroid 2004 BL86 and a tiny speck of a moon. NASA / JPL-Caltech via Slooh

"For people who want to look in the right direction you just have to find the brightest 'star' in the sky … and that's Jupiter," Slooh astronomer Bob Berman said. Then, he added, locate the star Procyon, which forms the winter triangle along with Betelgeuse and Sirius. The asteroid will be passing directly between the two stars for most of the evening, he said.

Observers in the Americas, Europe, and Africa will have the best seats during the asteroid's peak brightness, which is expected to last from 8 p.m. ET until about 1 a.m. ET Tuesday [Asteroid Quiz: The Space Rock Challenge]

— Shannon Hall, Space.com

This is a condensed and updated version of a report from Space.com. Read the original report. Follow Shannon Hall on Twitter. Follow Space.com on Twitter, Facebook and Google+.

If you capture a telescope view of asteroid 2004 BL86 during its flyby and want to share it with Space.com, you can send images and comments to managing editor Tariq Malik at: spacephotos@space.com.