Finding Comet C/2012 S1 (ISON)

As I noted on a post a couple of days ago, I’ve recently joined the Sierra Stars Observatory Network to try some deep space imaging with research-grade telescopes. I thought I’d see if I could use a 37 cm telescope on the SSON to photograph a comet that’s on its way into the inner solar system, called Comet C/2012 S1 (ISON). This comet is predicted to be visible to the naked eye in November of 2013. It’s possible it will be a very spectacular sight.

Right now it’s much more humble from earth’s position. Various web sites are listing quantitative observations already of the brightness of this comet, describing it as between magnitudes 15 and 16 – in other words, it’s really, really faint.

Anyway, the SSON system makes use of an extensive database of the locations of deep sky objects to allow users to photograph them robotically. I sent in requests for two exposures of the comet of 300 seconds each (without any filters) on the University of Iowa’s Rigel telescope in southern Arizona, two days apart. It took a while to pin down the location of the comet in each of the two resulting images. I had to use software that allowed me to determine the position of objects on each image, but there it was! In this image I’ve pasted the 16 April 2013 image onto the background of the 14 April image, so that both are visible in one frame. I’ve added the little cross-hairs to indicate which wee blob is actually the comet. The added text is from the “FITS” files that are sent down by the telescope’s computer. The first line is the date and local time at the start of each 300 second exposure. The second line is the Right Ascension of the comet at that time (the coordinate corresponding to longitude in equatorial coordinates, expressed in hours, minutes, and seconds); the third is the Declination of the comet (the coordinate corresponding to latitude, or degrees, minutes, and seconds above the celestial equator).

Comet C/2012 S1 (ISON) photographed on 14 and 16 April 2013 with the University of Iowa's Rigel Telescope.

Comet C/2012 S1 (ISON) photographed on 14 April 2013 (lower) and 16 April 2013 (upper) with the University of Iowa’s 37 cm Rigel Telescope. The photos were set up over the Sierra Stars Observatory Network (SSON). Taken as separate images and made into a mosaic with Photoshop Elements. The inset image in the lower right is the 14 April image without any reduction in scale if the whole image is displayed at 800 pixels across.

I was pretty excited to actually find the comet in these two frames! The moon was a bit of a problem on the 16th. It was not too far from the location of the comet in the sky that night, and as a result there’s some background glow on the later of the two frames (mostly cropped out of this composite image).

It will be interesting to observe the comet again in coming days and weeks, to see how much it’s growing in size and brightness as it comes into the inner solar system. In the inset on the image above you can just about make out that there’s already a tail visible. Images taken with larger telescopes are already showing a distinct tail.

The images that you can take for yourself with the telescopes on the Sierra Stars Observatory Network ( are carefully calibrated; if you wanted to use them for research purposes it would certainly be possible. For now I’m content to just see what I can do in terms of finding interesting objects and learning more about processing and improving the resulting images.

Copyright © 2013 David Allan Galbraith