In a rare bit of meteorological cooperation, metropolitan Boston had clear, albeit cold, skies for last night’s flyby of the asteroid 2007 TU24. And even as an observer experienced in hunting down moving targets, I had to stay on my cold toes to follow this speedy chunk of rock as it crossed nearly 3° of sky per hour.
The image here is a 10-minute exposure centered on 8:00 p.m. EST (1:00 Universal Time on the 29th), during which 2007 TU24 appeared to cross a Moon’s diameter of sky. Estimated to be about 800 feet across, the asteroid was then about 370,000 miles from Earth and closing. Closest approach wasn’t for another 7½ hours, when the distance would narrow to 340,000 miles, about 1.4 times the Moon’s distance.
Visually the asteroid was a little brighter than 12th magnitude and brightening about 0.2 magnitude per hour. Observing with a 7-inch reflector about an hour after this photograph was taken, my S&T colleague Tony Flanders estimated 2007 TU24 to be about magnitude 11½ — fainter than he expected. In fact, Roger Sinnott, another S&T editor, was unable to spot it with a 5-inch scope.
Did you look for this speedy interloper? If so, did you see it? Let me know via the Comments section below.