2012QG42, 13 September 2012
On the night of 13 September 2012, the recently-discovered near Earth asteroid 2012QG42 passed closest to the Earth. It seemed like a good opportunity to fire up my telescope for its first serious imaging for a very long time. The observation was challenging to say the least! At the time the asteroid was about 2.8 million kilometres distant, slightly fainter than 14th magnitude (same as Pluto) and moving at 48 arcminutes per hour. As a result, it spent just three seconds on each pixel of the CCD, not providing much integration time to collect photons! The image isn’t particularly good, but I was pleased to record anything at all. (The individual frames look better, especially when two are blinked together to show the asteroid's motion).
The telescope that I used was my old 30 cm reflector now working at F/4.1 with a Starlight Xpress H16 CCD giving a field of 42 arcmin square. The full image below (not the thumbnail) is 21 arcmin square with north up and west to the right. Twelve images of 30 seconds each were taken between 21.56 and 22.08 UT and stacked. During those 12 minutes the asteroid moved 10 arcmin (at position angle 285°) i.e. about half the width of the field. I get the impression that it was brighter at the start than the finish so maybe it has an irregular shape and is rotating relatively rapidly?
See SpaceWeather.com and skyandtelescope.com for more info.