After putting on an exciting show for a couple of weeks, Comet C/2020 F3 NEOWISE has passed Earth on its way back out of the Solar System – perhaps to return in about 6,000 years (space is big!).
The comet’s increasing distance from Earth and the continuous reduction in heating from the Sun are causing NEOWISE to fade in brightness over time. I’m not saying that you can’t see it anymore — it’s just a lot harder now. It will be visible in binoculars and telescopes for another couple of weeks, and then become a telescope-only target after about mid-August.
With decent binoculars, you should expect to see a small, greenish, fuzzy spot that looks different against any nearby stars. Unfortunately, the pesky Moon will be getting brighter and brighter in the evening sky this week, overwhelming the comet and hiding its faint tail, which will extend generally upwards, away from the Sun.
I’ve received quite a few messages from people around the world who are confused about how and when to see the comet — as if it’s just a momentary sight, like a shooting star. Perhaps that’s because images of comets make them look like they are zooming across the sky. In actuality, a comet moves relatively slowly, in human terms. It will appear near certain stars one night, then – as it flies through the Solar System, it will re-appear the next night shifted a little compared to those stars. On top of that night-to-night change in position, a comet will be slowly carried across the sky during the night – along with the nearby stars. That’s due to the Earth’s rotation.
In other words, once you spot the comet in your binoculars, you can go and grab grandma — or alert the neighbours — or take a bathroom break — because it will still be in almost the same spot when you get back.
Just make a note of where you found it. (A good tip is to stand in a particular location that lines the comet up with a building corner or a tree branch — then have your friend, or grandma, stand in that same spot.) By the way, if you see something rapidly crossing the sky, it’s a plane or a satellite — such as the International Space Station — and not Comet NEOWISE.
This week, Comet NEOWISE will only become observable in binoculars and telescopes once the moonlit sky darkens enough to allow you to see its faint glow. Then it will be carried lower and lower for several hours as the Earth turns. Things in space become harder to view when they are low in the sky because we are looking at them through a much thicker blanket of air, so try to see NEOWISE early.
From our point of view on Earth, the comet has been heading in a northeasterly direction — through the legs of the Great Bear, Ursa Major, and below the Big Dipper. This week, the comet will continue to climb a bit higher and shift to the left, away from Ursa Major’s bright stars. As the sky darkens tonight (Sunday), the comet will be located about three fist diameters (or 30 degrees) above the west-northwestern horizon (and somewhat higher than that by next weekend). Once the Sun has completely disappeared, you can safely sweep the sky for the comet with your binoculars.
After 10:30 p.m., the comet will become visible in binoculars, if your skies are clear and not too light-polluted. The easy way to find the comet is to look for the bright star Phecda high in the northwestern sky. It marks the bottom left corner of the Big Dipper’s bowl. The comet will be 1.5 fist diameters to the lower left of Phecda on Sunday and Monday evening.
Chris Vaughan is a science writer, geophysicist, astronomer, planetary scientist and an “outreach RASCal.” He writes Astronomy Skylights, and you can follow him on Twitter at @astrogeoguy. He can also bring his Digital Starlab portable inflatable planetarium to your school or other daytime or evening event. Contact him through AstroGeo.ca to tour the universe together.