Asteroid Flyover

Headlines were in abundance early this week about the flyover of the asteroid 2005 YU55, whose orbital path around the Sun took it inside the orbit of the Moon on Tuesday night (eg. see this article from Yahoo! News). This asteroid made a close pass by the Earth, being just 201,000 miles away. The asteroid was in no danger of hitting Earth, which NASA officials were quick to point out, but the fact that a 400-meter asteroid might come so close was enough to remind us all that a bad day is just one asteroid away. Having the opportunity to see an asteroid (or anything that's not man-made) move noticeably through the sky was enough to send me up to the observatory for a look.

I went up with two students, and a few folks from the public showed up as well. Using the 16" telescope we were able to identify the asteroid and track its motion across the sky for a couple of hours. Looking through the eyepiece, which had a field of view of about 1/2 a degree, the asteroid was moving quickly. Its motion with respect to the stationary stars was imperceptible until you saw it, at which point you couldn't NOT notice it moving. While it was not particularly bright, everyone present was able to see it. I was quite surprised at how rapidly it moved. I'm accustomed to seeing asteroids on CCD images make small streaks against the stars as they move across the CCD field of view, but seeing an object moving this rapidly (at its fastest it was moving at about 16 Moon-widths per hour) made quite an impression.

We attempted to take some images of it but experienced some trouble with the equipment. The CCD camera we were using was not one I had used before and we had difficulty identifying the field of view on the computer screen - it was smaller than the eyepiece. While we were unable to get any images of the asteroid, some had better luck. You can bet I'll be better prepared the next time something large flies by! By then perhaps we'll have the 1-meter telescope up and running for some real viewing.

For those who are privileged to see a beautiful sunset on the western horizon, keep your eyes peeled in the fading orange for a bright point of light above where the sun fell below the horizon. This bright point of light is Venus, our sister planet finally reappearing from behind the Sun. The eagle-eyed viewer might even see Mercury just next to Venus, although Mercury's brightness is quite a bit dimmer. For the next week, both planets move away from the Sun, being visible for longer and longer after sunset. After November 14, Mercury begins to move back toward the Sun, while Venus continues on in its wider orbit. The next time you have a clear view of the sunset, take a peek and see if you can spot both planets!