Comet C/2021 A1 Leonard

Comet Leonard is coming!

Comet C/2021 A1 (Leonard) is approaching the Sun – right now it’s only above the horizon in the early morning hours, but soon it will loop around and be visible in the evening. As of right now, you need a telescope to see it – it’s too dim even for binoculars. But it’s possible it will brighten further…

This is a video of the comet’s motion against the stars between around 5:15 – 5:45 this morning. It’s chugging along its orbit quickly! Watch for a photobomb from a pair of satellites in the upper-left of the video… I’m pretty sure those are StarLink satellites.

It looks a little weird, right? Your experience on Earth makes you expect that the tail would be pointing away from its direction of motion. But it’s not; the comet’s moving at a totally different angle along its orbit around the sun, while the wispy tail just follows along at its own angle. The tail just points away from the Sun, and with no air to drag on it and very little acceleration, the tail remains unaffected by its motion through Space. It’s a reminder of how our experience on Earth does not translate to Space. At all.

Long-exposure photography of comets is tricky; because it is moving so quickly relative to the stars, you need to produce an image of the starfield with the comet subtracted out, then add the comet back in, to avoid the stars appearing streaked over time. For the image below, I combined 30 one-minute exposures tracked on the comet with 10 one-minute exposures tracked on the stars. I didn’t have enough time to gather color data (should’ve gotten up earlier!) so it’s just black & white for now. (Processing color images of comets is even harder!)

EDIT!: I managed to get another half hour of clear skies, and gave color a go:

Comet C/2021 A1 Leonard

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