Let's say you're not the person in your social group who can ?? ??point out the astrophysical errors in the opening shot of the movie Contact. But let's also say you aresomeone who can easily spot the Big Dipper on a moonless night. In that case, you’re in the sweet spot to be wondering to yourself, "Hey um, what was the deal with that comet people were talking about the other day? Can I still see that?"
C/2017 K2 (PanSTARRS), sometimes called the K2 "megacomet," came closest to Earth on Thursday, July 14, at a distance of about 168 million miles, about 1.8 times the distance between Earth and the sun. Stargazers with telescopes have been tracking it for a while and watching its tail grow as it got closer, and now Earth is waving goodbye to the comet as it leaves. But if you’re reading this and it’s still summer, the now-receding comet is currently moving in a direction that will take it closer to the sun, and there’s a good chance you can still get a look at it if you own, or can borrow, a telescope.
What is C/2017 K2 (PanSTARRS)?
The comet seems to have originated in the Oort cloud, a likely collection of ice and rocks way out past the last of the planets at the edge of our solar system. The chunks are too faint to see — even with the James Webb telescope — which is why we can only surmise that the Oort cloud is there at all (It’s a pretty educated guess though, so no need to become an Oort cloud truther).
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The sun’s gravity occasionally coaxes one of these chunks out of its comfort zone in the Oort cloud and into our general neighborhood, and then it’s showtime. When the sun’s rays cause comets to release gases, that’s how they get their telltale glow, and occasionally become visible to the naked eye — though C/2017 K2 (PanSTARRS) is notlooking like it will be one of these cosmic attention-hogs any time in the near future.
But what makes the K2 comet unique is that while other comets appear, again and again, this seems to be this comet's first trip into our inner solar system. That unusual status seems to have made its gassy halo extra huge and bright since it would mean high concentrations of gas to be expelled.
Does that mean this comet is headed toward Earth?
Our research indicates that internet users who are searching for info about this comet are also checking to see if it’s going to kill us all — possibly because they recently watched a Leonardo DiCaprio movie on that topic. The short answer to that query is: Relax. A collision between this comet and Earth is not even a remote possibility. Yes, it was discovered by the ace comet spotters at the Hawaii-based Panoramic Survey Telescope and Rapid Response System (PanSTARRS), back in 2017, and that outpost is one of Earth’s watchful sentries, making sure no deadly “near-Earth objects” take us by surprise. But this was never flagged as a potential hazard. Besides, as I said before: it's now getting further from us, not closer.
So how do I see this comet?
If you’re new at this it might take some trial and error. You’ll be very lucky if you manage to peep the comet on your first night with your new telescope.
Start on any night when you can see the stars, and get used to finding the constellation Ophiuchus, the serpent bearer. When you find it, the comet is going to be a tiny speck in this constellation. You can rehearse this at your computer using the interactive sky chart on Skyandtelescope.org. With the help of an even more detailed star chart, you should be able to find the star cluster IC 4665 within Ophiuchus. Look for a cluster that kinda, sorta, if you squint, looks like it spells the word "Hi," and that's IC 4665.
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You’ll want the sky to be as dark as possible on the night you spot C/2017 K2 (PanSTARRS), so look just before moonrise — which you can figure out by looking at a chart of moon information for your region, or wait until the new moon. This might make the timing tricky, so figure out what works for you.
From our vantage point on Earth, C/2017 K2 (PanSTARRS) is a moving target within Ophiuchus, traveling across or near IC 4665, and moving a little less than the diameter of the full moon each night. Spotting it will involve aiming your ‘scope at the right stellar neighborhood, and then looking up, down, and all around. If you have a strong telescope, you might be able to see the tail, while the comet viewed through a weaker telescope will look more like a glowing fuzzball.
Or, since comets are unpredictable, there’s always the possibility that as it increases its proximity to the sun from now until December, some unknown chemical reaction on the comet itself will cause it to spontaneously brighten, making it even more visible. It could even become so bright that it can suddenly be seen without a telescope, as happened with the comet Holmes in 2007. Most sources, however, say you have until the end of the summer to spot it. So good luck out there this summer, and be sure to wear mosquito repellant.