Comet C/2007 N3 Lulin Still a good Target
- Comet C/2007 N3 Lulin is fading rapidly into the western sky. But it is still a good target, with a 20 arc minute long tail, magnitude about 9.5, and fairly high in Gemini. It also has an incredibly slow relative motion of only 0.01 arc seconds/minute, so you can take long exposures without blurring the comet.
Last night I imaged it under terrible seeing, but fortunately one doesn't need good seeing to image a comet. When I focus using AstroArt 3.0, a medium bright (mag 8 star) lights up just one pixel in focus mode. Last night the focus image was bouncing back and forth between 4 and 7 pixels! Probably 6 or 7 arc second RMS seeing. But I got a reasonable image at 5.0 arc seconds per pixel (binned 2x2).
My sky brightness was 19.0 magnitudes/ square arc second (measured with a Sky Quality Meter, as my 68 year old eyes aren't very sensitive any more). That translates into an NELM (naked-eye limiting magnitude) of about 4.7. I live 40 miles west of Chicago.
Images, associated data, and imaging notes at
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