2014-12-16

Christmas Comet Coming

After I briefly observed Christmas comet-to-be C/2014 Q2 Lovejoy visually last weekend, I managed to take some pictures last night. With the sky clear and dark, the comet was once again visible with the unaided eye and bright in binoculars. (Lovejoy is currently a southern hemisphere object, but will be visible from northern latitudes by the end of December.)

So I took out my camera and equipped it with a 200mm telephoto lens. As usual, I used an Astrotrac mount for unguided tracking. This is what the comet looked like after a 3-minute exposure (ISO 3200, f/5.6):

Unprocessed image of C/2014 Q2 (Canon EOS 600D, 200mm, 180s, ISO3200, f/5.6, 2014/12/15, 04:05 UT)

Crop of above image with three field stars and their respective magnitudes

The fuzzy, bright green coma looks surely brighter than some 6+ stars in the near vicinity, confirming that Lovejoy has reached 6th magnitude already. Visually, the comet appeared less bright than the picture suggests. In my 10x50 binoculars there was no trace of the tail, and naked eye the coma was at the edge of visibility - if your sky is light polluted, you won't be able to see the comet using your eyes only (yet). I estimate the coma to be around 6mag or even a little brighter. This is in agreement with other observations, e.g. these from Brazil.

In the stacked image (10x 360s, ISO 1600, f/5.6), the weak tail is a little more obvious. It's at least 2.5° long, that's 5 times the diameter of the moon in the sky. The diameter of the coma is >15':

Canon 600D, 200mm lens, 10x 360s, ISO1600, f/5.6

Canon 600D, 200mm lens, 10x 360s, ISO1600, f/5.6
Update: Here is a color-enhanced version of the same image. The comet's coma (like most cometary comae), is very green, while the tail has a more reddish color. The green light in many comets stems from emission of CN (cyanogen), C2 (two carbon atoms), and C3 (three carbon atoms). C2 emits green light, the other two shine blue. So even without taking a spectrum, on can conclude that the Cemission lines at 470 and 510nm will be very prominent. The red color is probably due to dust particles reflecting sunlight. Find more on comet colors here.

Colorful comet. The coma is bright green, while the tail has more reddish color
The chip in my camera (like the human eye) is much more sensitive for the green than red part of the spectrum. This is why the tail is so much harder to see (and image) than the coma. (Ok, and because the coma really is denser and thus brighter than the tail.)

C/2014 Q2 Lovejoy is currently moving northward through Puppis, a constellation which passes right through zenith after midnight here southern in Chile. It will be traveling through Lepus and Eridanus in a few days. By January 2015, it will be some degrees Southwest of Rigel, Orion's bright foot star and thus visible for any place on Earth. Sky&Telescope has observing tips and a finder chart.

Clear Skies!

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