Three Comets in the Dawn

While comet C/2012 S1 ISON is getting all of the attention, it is not the only comet currently visible. There are a couple other good comets available to observe or photograph. On Sunday morning I tracked down and photographed three comets.

Comet ISON is sharing the stage with comet 2P/Encke and comet C/2013 R1 Lovejoy. All three are bright enough to be spotted in a small telescope. Encke was about magnitude 8, Lovejoy and ISON were both about magnitude 5 on Sunday morning.

Despite following comet ISON for the last year, I had never actually observed it myself. Attempts to change this repeatedly ran into problems, either work commitments or bad weather. Over the last month cloudy skies have been more common than clear, even the big ‘scopes on the mountain losing a large amount of time to poor conditions.

The forecast and satellite photos held out hope for Saturday night and Sunday morning, a promise of clear skies. Unfortunately the Moon was also full, this would create problems.

Thus I packed up the astrophoto rig, the iOptron mount, TV-76 and a pile of camera gear, departing for Hale Pohaku at midnight. All of the comets I hoped to photograph are dawn objects, arriving at HP at 1am allowed be time to setup and capture each comet as it rose over the horizon.

The clouds did hold off, a few wisps of cirrus did cross through my frames. It was the moonlight that interfered badly. My hope was that above the inversion level there would be little haze in the clear mountain air to scatter the light giving a better view. This only partly worked. Exposures were limited to about 30 seconds, anything longer and the background overexposed.

Still, I set the camera shooting, perhaps sheer quantity of frames would make up for the quality. With short exposures it would be easy to get a lot of exposures in the short time available.

Beside the moonlight the morning was glorious. The comets visible in the binoculars. There was almost no wind and the temperature was surprisingly warm. As dawn approached a few other comet watchers showed up.

Comet Lovejoy was already up when I finished setting up the photo gear. Comet ISON did not rise until 0409, just an hour before twilight would begin.

Comet Encke was the last target, rising in the already bright glow of dawn just above the planet Mercury. I could be certain of the comet in the binocular field, I just set the telescope and camera on the right place and fired. Indeed there was a point of light in the correct position. There was only time for a few frames, so I set a short sequence of 10 second exposures and hit start.

When I first looked at the photos I despaired. How could I retrieve anything from the wash of moonlight? I could not bear to try for a couple days. Thursday I finally made the attempt, the signal to noise was horrible, but I has a lot of frames, 80 exposures on ISON and almost as many for Lovejoy.

It took several hours to process that many exposures. Fortunately much of that is automated, I can chose my settings and walk away from the computer for a while. In the end I managed a half decent photo of ISON, not the complete disaster I first feared. I have yet to process the Lovejoy image, at least this comet will still be high in the sky when the moonlight fades. Even Encke shows up faintly in the image, despite being so low in the glow of dawn.

This coming weekend offers another opportunity or perhaps later in the week. The moonlight is fading with the waning Moon, comet ISON is also brightening quickly. On the other hand the comet is rapidly getting lower in the dawn.