CCD Limits, or How I Imaged Comet Shoemaker-Levy 9
by Bob Sandness

It was supposed to be easy. After all, Shoemaker Levy was about 13th magnitude and that was well within the grasp of a C14 telescope and a SBIG ST6 CCD camera. But it didn't turn out that way.

The first challenge was to find the comet. Using the coordinates in Astronomy magazine, I tried a few short exposures (100-200 seconds). Nothing but stars and faint galaxies showed up on my laptops glowing display. Convinced that I must of just missed it, the next night I took a series of exposures (200 seconds each) to create a mosaic. Once again no sign of Shoemaker-Levy 9.

At this point I realized that there were two possible explanations of my failure: I was imaging the wrong area or the comet was a lot fainter than I thought it was.

In order to verify the comets position I did what any seasoned NYAA member would do -- I called Tony Ward. After he gave me a 10 minute tutorial on how to use Dance of the Planets, I had the correct coordinates.

That night I imaged the target area with 3 separate 800-second exposures using the ST6 Track-and- Accumulate mode. Once again nothing was visible on the laptop's display

The next morning I transferred the 3 images to my desktop computer and examined them with Hidden Image. On the monitor two of the three images showed a faint streak with 3-4 diffuse "blobs". Eureka!

Later that day Danny Driscoll and Andreas Gada also viewed the images and confirmed that I wasn't employing wishful thinking.

The image shown here is the result of combining two 800-second exposures and performing further image processing, including the use of Hidden Image. If the information in the August issue of Astronomy magazine is correct, then the nuclei are between 19th and 21st magnitude! Since the C14 collects about 5 photons per second from a 21st magnitude object, I guess that the result is not bad for the light polluted skies of King City.

Thanks again to Tony Ward for his help and to Doug George for his suggestions and efforts in processing the image.


North York Astronomical Association Resources