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SYFY WIRE Bad Astronomy

Ride Along With the Halloween Asteroid TB145 as It Glides Across the Stars

By Phil Plait

On Halloween, the 600-meter-wide asteroid (or dead comet?) 2015 TB145 slid past the Earth at a distance of about 480,000 kilometers. That’s pretty close as interplanetary distances go, but still comfortably farther than the Moon from Earth.

Not only were we in no danger from this rock, but it provided eager astronomers an opportunity to observe it. Radar observations with the huge Arecibo telescope showed it to be round—skull-shaped, in fact!—and rotating once every five hours or so.

But you didn’t need a huge professional observatory to see it. The asteroid was bright enough to see in smaller ‘scopes, and a couple of lovely videos of TB145 have already popped up.

The first is pretty dramatic: It was taken by friend-of-the-BA-blog Gianluca Masi using a 43 cm (17”) telescope with the Virtual Observatory Project. Over nearly three hours he took 276 frames, keeping the asteroid centered in each one. The exposures were long enough—and the asteroid’s motion rapid enough—that stars are streaked in the images.

It feels like you’re riding along with the asteroid, doesn’t it? As the video progresses, the asteroid got apparently closer to the Moon in the sky, so you can see the upper right corner getting brighter as the Moon approaches.

The Virtual Observatory Project frequently does live observing, and does a great job of bringing the heavens down to Earth. Keep your eye on the Upcoming Events page, and, because they’re a volunteer project, consider throwing some filthy lucre their way.

The second video is from Jerry Hilburn at the San Diego Astronomy Association’s Tierra del Sol observatory. It shows a more standard view, tracking the stars as the asteroid glides past them. Each exposure was 10 seconds long, with a five second gap between them, showing a total of 12 minutes of real time:

Again, the asteroid was near the Moon, but Hilburn removed most of the streaking and glare individually in each exposure. Nicely done.

When I was younger I could only dream of seeing movies of asteroids flying past the Earth, but now we can not only make them but get them online and visible to the whole planet within hours. It’s thrilling to me how much this technology has revolutionized modern astronomy!

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