Click to enlarge
Tonight, the evening of 2020-07-18, around 21:00 UTC, I finally got the chance to observe and photograph comet C/2020 F3 (NEOWISE), the Great Comet of 2020, on the first night of (kinda) clear sky after the comet appeared in the evening sky. Even though the sky was visibly milky, with thin haze reflecting distant lights, after becoming dark adapted, the comet was an easy naked-eye object near the northwestern horizon (which is elevated due to the Jura mountains in that direction). Through binoculars (Canon 15×50mm image stabilised) the star-like nucleus and coma were well-defined, and the dust tail extended until it was lost in the murky sky. I was unable to pick up the dimmer, straight, blue ion tail either with the unaided eye or binoculars.
To photograph the comet, I set up my Leica M240 rangefinder digital camera with the Leica Noctilux 50 mm f/0.95 lens on a tripod. This is a very fast “normal” lens, which means it provides a field of view comparable to the human eye, but its light capturing capability far exceeds that of the eye. The picture you see here is comparable to what you’d see looking directly at the comet, if your eye were much more sensitive than a camera made of meat can possibly be.
I made a variety of exposures using ISO speeds between 400 and 3200 and exposure times ranging from 1 to 8 seconds (the maximum available on the M240), with automatic subtraction of a dark frame for noise reduction. The picture I chose to show here was taken at ISO 800 with an exposure time of 6 seconds at F/0.95. Leica lenses have a Teutonically-precise stop at the infinity focus setting, so for astrophotography there’s no fiddling with focus: you just turn it to the infinity stop and the image is perfect. For a lens with such an insane focal ratio, the Noctilux performs remarkably well off-axis, but I have cropped the image to elide some slightly potato-shaped stars in the corners of the full frame (which contains no useful information in any case).
It is clear from stretching the image into less aesthetic presentations that the comet’s tails extend well beyond what is captured here. In a darker, clearer sky with a longer exposure, the comet would be even more spectacular. In this picture, you can see the ion tail extending straight to the left of the broad, curved dust tail. It doesn’t jump out at you, but it’s clearly there, especially when you click the picture to view the enlargement. The ion tail, made of gas emitted by the comet, energised by solar radiation, and entrained by the solar wind, is blue, but the hue isn’t apparent in this picture: it’s just a greyish, maybe slightly blue, straight ray.
For observers in the northern hemisphere, this apparition is a superb chance to glimpse a magnificent comet which is easy to find, observe, and photograph. I remember when my father pointed out comet Arend-Roland (C/1956 R1) when I was a little kid. If you have small children, now’s your chance to get them to look away from their screens for a moment and up to the glories of the heavens. It may change their lives, and those of their children and descendants.
If you observe the comet, please describe what you saw and, if you get any photos, post them in the comments.
Here is a NASA guide to spotting the comet in the coming days. If you miss the comet on its current swing around the Sun, it’ll be back in around 6800 years.