Posted tagged ‘asteroid 2007 TU24’

Asteroid 2007 TU24’s close encounter with Earth

January 28, 2008

Asteroid 2007 TU24, discovered only last October, skimmed past the Earth last night at 3:33AM EST (0833 UT) at a distance of 344,000 miles.  It didn’t get as much media attention as I’d expected, and even the astronomy magazines have given it minimal coverage, if any.  Sky & Telescope had a good article which piqued my curiosity.

So, I collected all the data I could find and prayed for clear skies. I expected to be disappointed, so I created a really cool animation of the pass from the point of view of the asteroid, and sped it up 30,000 times. It’s fun to watch.  Unfortunately, WordPress.com doesn’t yet offer a way to include high-quality videos in blog entries, but here’s the best I can do for now.  Sorry about lousy quality and advertising.

OK, that experiment worked out very poorly.  When I watched it, the movie after mine was two young ladies in a smoking fetish video, which I don’t want in my blog.  So here is a link to the good version of the video.  You’ll need QuickTime to watch it.

Wicked rad bonus animation of TU24 zipping by Earth

The illustrations I’d seen showing TU24’s movement as a graceful arc across the sky weren’t and couldn’t be accurate enough to spot the asteroid.  I thought this might partly explain the lack of coverage on TU24—it’s so close to Earth that it’s impossible to print a simple finder chart.  Parallax, an effect of the geometry between two observers’ separate positions on the globe, an asteroid only 44% farther from Earth than the Moon, and the vastly more distant background stars, would shift TU24’s apparent position in the sky too much for even a single US chart to be accurate enough.

Starry Night to the rescue.  Unfortunately, the publisher didn’t release updated with orbital elements for 2007 TU24, so I entered the data myself from JPL’s HORIZONS site and studied the asteroid’s movement for good viewing opportunities.  I read anything I could find in the newsgroups and mailing lists.

We got lucky near Boston MA, and the night sky on 1/28 wasn’t clouded in, as it has been most nights.  So I shoveled off the back deck and put all my optics out there to cool down.  It was 30°F at 4PM, and was supposed to get down toward 20°F.  I also prepared everything I could think of, and left a pile of gear that wouldn’t need cooling just inside the back door.

My plan was to use Starry Night and my laptop to get the Celestron 8i pointed near TU24, then star-hop around to home in on it, using the laptop to track the movement of the asteroid.  This didn’t work.  First, the scope and the program were about a degree apart, and I couldn’t get them to agree.  Second, and I only found this out today, even the latest orbital elements from JPL were another degree off from where it really was in the sky last night.  (Sky & Telescope ran another article today, with pictures taken from Boston.) So, after hours of prep work and almost three hours in the cold, I came within a degree or two.  It’s a little comforting that only two of the three S&T editors could find it. (…though one was using a 5″ scope.  Shhhh!  My unconscious might be listening…)

I learned a few important lessons.  First and foremost, though I’ve done below-freezing observing before, I forgot the cold-weather hiker’s motto: Cotton Kills.  I only had cotton socks on under my boots, and around 10:30PM my feet started hurting in a way I knew wasn’t good.  They felt so cold they felt wet, and I knew I had to get indoors as soon as possible.  Long story short, after 10 painful-to-the-bone minutes having them in lukewarm water, there were no lasting effects.  But, my socks were wet!  From now on, it’s back to poly pro undersocks, and my wicking, hiking socks over them.  How could I forget?

The second lesson was one I had come across in my reading, but mostly ignored.  That is, Don’t Trust Near Earth Orbit Predictions!  An experienced NEO spotter and Starry Night user had said to spot a place in front of the predicted pass, and wait 10 minutes or so for it to come into view.  After an hour of futzing with the scope and the laptop, I took the advice, but to no avail.

The third lesson was, don’t use too-high magnification.  With my 35mm Nagler, I had about a 1° field of view, which was too small. Next time, I’ll use tripod-mounted astronomy binoculars to locate the object.

The last lesson was, Practice Practice Practice!  It was fun and I’ll definitely do it again.  But this isn’t for everyone.  It takes a lot of patience, and even more prep work than usual. That’s probably the real reason why it wasn’t in a lot of magazines.