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How And When To Watch The Giant K2 Comet Swing Past Earth This Week

For once the rumors are true, it really is rather large. 


Katy Evans

Katy is Managing Editor at IFLScience where she oversees editorial content from News articles to Features, and even occasionally writes some.

Managing Editor

A blue fuzzy picture of comet K2
Comet C/2017 K2 PANSTARRS was the furthest known active comet ever until Bernardinelli–Bernstein took its crown. Image credit: NASA/ESA/D. Jewitt (UCLA)

One of the furthest known active comets ever spotted is set to make its closest approach to Earth on Wednesday, and you can watch it all live – and yes, it's rather large.

First spotted by Hubble in 2017, Comet C/2017 K2 (PANSTARRS), or K2, was thought to be the most distant active comet ever discovered when it was spied lurking in the outer Solar System. That record was smashed by megacomet Bernardinelli-Bernstein earlier this year, but K2 has been steadily making its way towards us over the last five years. Now it's set to zoom just 270 million kilometers (168 million miles) past Earth on July 14 as it continues its path through the inner Solar System. 


There's quite a lot of uncertainty around how large the comet's nucleus (the solid central dirty snowball bit) is, but current estimates range from 18 kilometers (11 miles) to 160 kilometers (100 miles). Either way, that's a large comet – but if it's on the larger end of the estimates, it's one of the largest known comets yet, alongside Bernardinelli-Bernstein and Hale-Bopp. A close flyby will help astronomers narrow that margin.

K2's tail, on the other hand, is definitely huge. Estimates vary again, but we're looking at something between 130,000 and 800,000 kilometers (81,000 and 500,000 miles). 

During its closest approach, it's set to brighten to a magnitude of 8 or 7 (the lower the number, the brighter), although it will probably still be too dim to see with the naked eye. Telescopes should have no problem though, and it will be visible for the rest of the summer. 

If you don't have a telescope, you can watch it swing by with the help of the Virtual Telescope Project which is live-streaming it from 6.15 pm ET (10:15 pm UTC) on July 14. 


As K2 continues on its perihelion (its closest pass to the Sun), its behavior may change. It may become more active as the Sun heats up the icy nucleus, and it could become brighter – or even break apart. One thing is for sure, expect a few spectacular images of it from both professionals and amateurs over the next few weeks. Comets this big love to put on a show.


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