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 that you are a person who can easily spot the Big Dipper on a moonless night. In that case, you’re in the sweet spot of wondering to yourself, “Hey, um, what was the deal with that comet that people were talking about the other day? Can I still see this?’
C/2017 K2 (PanSTARRS), sometimes called “megacomet” K2, made its closest approach 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 some time, watching its tail grow as it approaches, and now Earth is waving goodbye to the comet as it departs. 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’ll still be able to catch a glimpse of it if you own, or can take borrow a telescope.
What is C/2017 K2 (PanSTARRS)?
The comet appears to have originated in the Oort cloud, possibly a collection of ice and rock far past the last of the planets at the end of our solar system. The pieces are too faint to see – even with the James Webb telescope – so we can only assume that the Oort cloud is there at all (this is a pretty educated guess though, so no need to become a cloud realist of Oort).
The sun’s gravity occasionally forces one of these chunks out of its comfort zone in the Oort cloud and into our common neighborhood, and then it’s show time. When sunlight causes comets to give off gas, they get their telltale glow and sometimes become visible to the naked eye—though C/2017 K2 (PanSTARRS) doesn’t look like one of those cosmic eye-catchers anytime soon.
But what makes comet K2 unique is that, while other comets appear time and time again, this appears to be the first trip of this comet into our inner solar system. This unusual condition appears to have made its halo of gas extremely large and bright, as it would mean ejecting high concentrations of gas.
Does this mean this comet is headed for Earth?
Our research shows that internet users looking for information about this comet are also checking to see if it’s going to kill us all – possibly because they’ve recently seen a Leonardo DiCaprio movie about it. The short answer to this question is: relax. A collision between this comet and Earth is not even a remote possibility. Yes, it was discovered by comet watchers at the Hawaii-based Panoramic Telescope for Survey and Rapid Response System (PanSTARRS) in 2017, and this outpost is one of Earth’s watchful sentinels, ensuring no deadly ‘close-to Earth objects’ surprised us. But it was never flagged as a potential danger. Also, as I said before: it’s getting further away from us now, not closer.
So how do I see this comet?
If you are new to this, it may take some trial and error. You’ll be very lucky if you can catch a glimpse of the comet on your first night with your new telescope.
Start every night when you can see the stars, and get used to finding the constellation Ophiuchus, the Ophiuchus. When you find it, the comet will be a tiny speck in this constellation. You can rehearse this on your computer using the interactive sky chart at Skyandtelescope.org. Using an even more detailed star map, you should be able to find the star cluster IC 4665 in Ophiuchus. Look for a cluster that kind of, sort of, if you squint, looks like it spells out the word “Hello,” and that’s IC 4665.
You’ll want the sky to be as dark as possible the night you spot C/2017 K2 (PanSTARRS), so look just before moonrise—which you can tell by looking at a moon information chart for your region, or wait until a new moon . This can make timing difficult, so find out what works for you.
From our point of view on Earth, C/2017 K2 (PanSTARRS) is a moving target in Ophiuchus traveling through or near IC 4665 and each night moves slightly less than the diameter of the full moon. Spotting it will involve aiming your scope at the correct star neighborhood and then looking up, down and around. If you have a strong telescope, you may be able to see the tail, while the comet viewed through a weaker telescope will look more like a ball of light.
Or, since comets are unpredictable, there’s always the possibility that as it increases its proximity to the sun between now and December, some unknown chemical reaction on the comet itself will cause it to spontaneously brighten, making it even more visible. It may even become so bright that it can suddenly be seen without a telescope, as happened with Comet Holmes in 2007. However, most sources say you have until late summer to spot it. So good luck this summer and don’t forget to wear mosquito repellent.
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