Last night I watched an asteroid --- 2004 BL86 --- drift past the Earth. There was never any danger of a collision and it never got closer than about 3x the distance of the Moon. Nevertheless it was an interesting event to watch through the telescope. The asteroid was tracking north through the evening sky. At around 7.30pm, when I arrived home from work, it was too low in the southeast sky in Hydra. As the evening went on it raced north towards the constellation Cancer.
The animation below was made from frames taken over a ten minute period at around 9.30pm. The asteroid moved across a patch of sky about the size of the full moon during this period.
I stacked the images to make this picture:
I'm not sure why the asteroid has a strong green colour! It may be that the presence of moonlight in the sky messed up the colour balance during post processing.
Just to put this into some kind of perspective: the asteroid is about half a mile in diameter and it was around 1 milliion miles away when I took the pictures. Shining at around 9th magnitude, the asteroid was much too faint to be seen without optical aid. I saw several articles on astronomy and science websites suggesting that binoculars would have been enough. The fact of the matter is that at least a small telescope would have been needed by most observers unfamiliar with searching for faint objects.
Radar surveys of the asteroid carried out yesterday showed this tiny asteroid had a moon!
This is second time I've caught an asteroid close approach. I was lucky enough to catch the even closer approach by an asteroid called Duende (formerly 2012DA14) in 2013.
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Dr Adrian Jannetta. Amateur astronomer, maths teacher and science enthusiast.