Wednesday, November 30, 2011

Eunomia Traverses California Nebula

While post processing a set of images of the California Nebula (NGC-1499) that I collected on Nov 28, I noticed a moving object in the field of view. This image shows the position at 05h00 UTC and the relative path.

I computed the motion relative to the star-field to be about 40 arcsec/hr. The corresponding absolute motion across the sky was too slow for a low earth orbit satellite and too fast for a geosynchronous satellite. I gathered it was likely a solar system object. On the other hand, comparing the brightness to other stars in the field, I estimated this object to have magnitude between 7 and 8, larger than expected.

I was not sure how to cross check this against know objects but some colleagues from the Austin Astronomical Society helped me out. Harden pointed me to the Central Bureau for Astronomical Telegrams (CBAT) and Mike checked Otwell's Astronomical Calendar and found an entry for the asteroid "15 Eunomia" stating that it would be at opposition on Nov 28 in the California Nebula at magnitude 7.9. Sounded like a match! I later found a published graphic of the path of the asteroid further confirming the match. In wikipedia article I read that 15 Eunomia is the largest stony asteroid and was discovered in 1851 by Annibale de Gasparis ... I little earlier than my observation.

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