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Friday, April 10, 2009


Comet C2009 G1 - Congratulations Jiangao Ruan

UPDATE: Confirmation of the comet from Earthside observer K. Kadota in Japan. See this MEPC with updated orbital elements. And I have made a spotters map of the eastern morning sky with the updated elements.

I have no idea whether Jiangao Ruan examines his STEREO images in the small hours of the morning, or looks at them over breakfast, as Comet Al does, but on Wednesday Jiangao sent a message to the stereo hunters group asking if a faint blob he saw transversing the STEREO H1b camera images was a known comet.

In quick time the stereohunter community swung into action, we confirmed the object, and in rapid time eliminated 209P/LINEAR, C/2008 T2 - Cardinal, P/2002 JN16, 2009 F6 (Yi-SWAN) and 446 Tisiphone, the only objects vaguely near the unknowns position, as candidates. This looked good as a new comet.

Karl Battams sent in a whole bunch of measured positions to the MPEC, and we waited. While we waited, we tried to work out where the comet was as seen by an observer from Earth, to alert the local telescopic community. Then the news came back, Jiangao's comet was named as C/2009 G1 (STEREO). And there was much rejoicing. To my knowledge this is only the second comet to be discovered first in the STEREO imager (as opposed to Comet Al's recovery of C/2003 K2), they are usually picked up in SWAN or SOHO first.

The announcement and orbital elements are here http://www.cfa.harvard.edu/mpec/K09/K09G30.html and I have a printable PDF of the comets location here (yes, it's labeled G2 on my map, fumble fingers and no time to re-edit). The Comet is really magnitude 10 (and not likely to get much brighter), rather than the 12 indicated on my map (limitations of the way I put data into SkyMap). My PDF map also shows he location of Juno and 2009 G1 from the point of view of the H1b camera, and my (very bad) estimate of where the comet would be as seen from Earth),

Sadly the comet is currently in a very unfavorable position, very low to the eastern horizon in the morning, with the full Moon in the sky, this will make it hard to see for several days. It will get better. By the 18th of May, the comet will be 26 degrees above the horizon at astronomical twilight (as seen in Australia), with a last quarter Moon in the sky.

My animation of the comet is here, the comet is near the top right, and the asteroid Juno is near the bottom centre. Adam Hurcewicz has an animation here.

Congratulations again Jiangao!

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Outstanding new discovery and I honor the people who were involved.
Great job on the discovery, I imaged Comet C/2009 G1 STEREO a few hours ago from Chile. Animation
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