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Goodbye to Comet C/2020 M3 (ATLAS)

2020 December 30
by Russ

This animated GIF of Comet C/2020 M3 (ATLAS) consists of a sequence of six images aligned and overlaid one on top of the other. Each image is made up of a stack of eleven 10-second subimages. The 40-minute sequence was taken on December 27, 2020, between 02:49-03:31 UT with an 8” Celestron SCT (203mm f/10) operating at f/5 and a ZWO ASI224MC CMOS camera. The field of view is 17×12 arcminutes (0.28×0.20 degrees). North is up. East is left. You can see a full-size version of this animation here.

Although I had just observed and imaged Comet C/2020 M3 (ATLAS) seven days earlier, I was drawn back to it again. At first I thought it was because the moon was high and bright in the sky washing out faint galaxies and nebulae and making them unsuitable targets for the evening’s observing session. I also thought it was because the wind was really gusting, buffeting the telescope and making long camera exposures impossible. In retrospect, I realize it was because I was fascinated by watching the live images build on my screen showing this small fuzzy visitor in real time as it silently moved against the background of stars in the constellation Auriga back to its realm in outer solar system.

Comet C/2020 M3 (ATLAS) won’t be back this way for 139 years.  Its elongated elliptical orbit takes it out to 27 astronomical units from the Sun, or just inside the orbit of the planet Neptune, which orbits at 30 astronomical units (2.8 billion miles or 4.5 billion km).  At the time this animation sequence was captured, the comet was 50 million miles (81 million km) from Earth.

This animation shows Comet C/2020 M3 (ATLAS) at magnitude 13.0 (measured in the green channel), considerably dimmer than the magnitude 11.8 I measured seven days earlier.  As Comet ATLAS continues to recede from us on its run back to the deep reaches of the solar system it will continue to fade.  Soon, it will only be visible to the largest telescopes as a faint dot.

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