Last night, or, really, early this morning, I went out again to try to get images of Comet Lovejoy. I chose to do it now because, first, the Moon was no longer in the sky and, second, since Comet ISON did not survive its trip around the Sun, (which was sad), Lovejoy was the next best bet. Finally, this looked like the only clear night for the forecastable future, and I didn’t want to miss my chance.
What a difference ten days makes! The comet looked considerably brighter, at least partially because of the lack of moonlight, but also because it, too, is heading for the sun. It will reach its closest point, perihelion, on December 22nd, but it won’t get nearly as close as ISON did — tens of millions of miles, rather than hundreds of thousands. Still, what that means is that it is getting lower in the sky each day, closer and closer to both the horizon and to the brightening dawn. Lovejoy was actually closest to Earth on November 19th, the last time I imaged it, but the sun at that date hadn’t worked on it as long or as intensely.
Ten days also made a huge difference in the weather here in western Wisconsin. When I took the last image, the temperature was right around the freezing point. Skies on that day were also very dry and free of haze. This morning, it was hovering around -3 degrees Fahrenheit (-19 C)! The ‘transparency’ — basically, the amount of water in the air — was quite high, so stars (and comets) did not appear as bright as they otherwise might have. And there was a steady breeze, too. That difference in temperature made it harder on me, but also on both the electronic and mechanical gear. The grease used in my old Vixen Super Polaris mount apparently is not rated for temperatures much below freezing. I was glad to find that its motors, for tracking the sky as the Earth turned, kept moving just fine. But turning it by hand to get it aimed correctly was very difficult, even when the clutches were completely loose! Tightening and loosening various locking nuts and bolts was also hard, but mostly because I often had to remove my gloves to do it, and my fingers instantly froze.
My Canon T1i DSLR camera worked just fine, but only because I had brought along my external power source, a nifty little device with a cord that has a battery-shaped insert that goes into the camera. I plugged the cord into a small 12 volt DC to 110 volt AC inverter, and plugged that into my big 105 Amp-hour 12 volt marine battery. The fan on the inverter did not like the cold, either. It made loud, ominous noises while in operation, but never stopped working. The camera’s internal battery would quickly have gone dead from the cold, and, though I keep a spare one warm in my pocket, changing batteries in this cold, which would have required some interesting contortions, was something I’m glad to have avoided.
I used a small intervalometer to take the actual images. It plugs into a port on the camera’s side, and has various settings shown on a small LCD screen. You can set how long you want each shot to be, how long an interval between each shot, and how many shots to take. I experimented to get the best exposure, but by the time I settled on about 1 minute 40 seconds, the screen on the intervalometer was acting funny from the cold. (Two minutes each would have been better, but the wind over that long made the images too wobbly; I had to throw out three of ten as it was, and the stars in the final image are still not perfectly round.)
It was a nice little adventure, and when I was finished, everything had a layer of frost on it, but nothing failed. I could have asked for more, but didn’t really need it.
Technical information: Camera: Canon T1i (500D), unmodified. Lens: Nikon 180mm ED f/2.8 (with a 72-55mm step-down ring mounted to make it about f/3.5; done to prevent the aperture blades on the lens from causing points on brighter stars). Mount: Vixen Super Polaris EQ from the 1990s, with dual drives (non go-to). Best seven of ten light frames, 101 seconds each, unguided. Taken between 5:44 and 5:55 CST. Ten darks of the same length. Processed in DeepSkyStacker, and stretched in Photoshop CS2.