Comet 73P Schwassmann-Wachmann
A cosmic speedster
May 7, 2006

Comet 73P Schwassmann-Wachmann was imaged at 2:00 am on Sunday, May 7.  Even though the comet is reasonably bright, about 7th magnitude (similar to a dim star) it is difficult to photograph because it is moving so rapidly through the field of view.  The top image above was made in five minutes and then processed to make the comet's head, the coma, look somewhat circular.  The second image is of ten minutes duration and shows how quickly the comet is moving relative to the distant background stars.  In this case it works out to about 14 arc seconds per minute.  In order to mitigate this problem some photographers track the comet instead of freezing the background star field.  This gives a nice tight comet image, allows longer exposures and can reveal more detail in the comet's tail, but it also has the effect of streaking the background stars.  Another possibility would be to use a very large telescope with a low focal ratio so that ample light could be collected in a very short time, say under one minute.

Date: May 7, 2006
Location: Cupertino, CA
Scope: Takahashi FS102 @ 600mm
Guiding: Vixen 60mm refractor with SBIG ST-4
Mount: Losmandy G-11
Camera: SBIG ST2000XM
Filters: Custom Scientific in FLI CFW
Exposure details:
  Top: Luminance filter, 5 minutes
  Bottom: Red filter, 10 minutes
 Processing: MaximDL for calibration 
PSCS   for final processing