The comet C/2017 K2 is due to reach its closest point to Earth on Thursday, and it will be possible to see it either online or in-person—provided you have a telescope and dark skies.
The comet has attracted scientists' attention for years since it was first discovered in 2017. At the time, the comet was notable since it was the most distant active comet headed towards the inner solar system that had ever been seen, and was surrounded by a cloud of dust 80,000 miles wide.
Comets are huge chunks of ice and rock that float around the solar system. They are known for their bright, characteristic tails caused when they are close enough to the sun that they heat up and begin expelling gas. Comets that do this are considered to be active.
Comets are of interest to scientists generally because they represent pristine leftovers from the early days of the solar system and could provide clues as to how it formed in the first place.
Scientists think that K2 has come from a distant, remote region of the solar system known as the Oort Cloud and has been traveling towards the sun for millions of years, so it could be interesting to observe.
K2 is due to reach its closest point to Earth on Wednesday at 11:09 p.m. EDT, according to space news site Space.com, which cites data from NASA's Jet Propulsion Laboratory.
While this may conjure up images of a sky brightened by a beautiful comet gliding overhead, it's important to note that the comet will not actually come particularly close to Earth at all—in fact, NASA's calculations of its predicted path show that it won't even get past the orbit of Mars before it swings around the sun and backs out of the solar system again.
That's worth bearing in mind considering some news reports suggesting the comet may be some kind of threat to Earth—it isn't.
In regards to viewing, since the comet will be even further away than Mars at its closest point to Earth, it probably won't be visible to the naked eye at any point. Astronomy website EarthSky predicts the comet may reach a brightness of magnitude 8 or 7, and the faintest naked-eye star we can see is about magnitude 6—the lower the number, the brighter the object.
However, it is perfectly possible to view the comet at night using a small personal telescope. In fact, it's been possible to view the comet this way for weeks.
To get a telescope view of C/2017 K2 on Wednesday and Thursday, it might help to use the browser app Stellarium, which assists in locating night-sky objects. The below images show that in the early hours of Thursday, the comet will be located roughly near the star 30 Ophiuchi, which appears to the comet's lower left, and above the globular cluster Messier 10.
Additionally, the comet's coordinates are set out in the information box on the left of the image. The lower image shows where the comet will be relative to the horizon.
For those who do not have access to a small telescope, it will be possible to observe the comet online the following evening via a live stream hosted by the Virtual Telescope Project.
The stream is due to start on Thursday at 22:15 UTC (18:15 ET) on the Virtual Telescope Project's WebTV page here.
