This object was discovered from Hawaii in October, when it was originally thought to be an asteroid. But further study by astronomer Ari Heinze proved that it's a comet.
It will pass around 20 million miles from Earth on January 4th, on its way to perihelion on February 21st. It's not going to be very bright (around 8th magnitude), but should still be visible in our telescopes.

I first detected it from New Mexico a couple of weeks ago:
But it's brightening rapidly, as can be seen from these more recent images which I got from the COAST facility on Tenerife:
And it's so fast-moving that it shows trailing even over 150 seconds, so on the following morning I halved the exposure-time:
It's an early-morning object at the moment, but is moving very quickly across the sky, so it will be visible all night in the first half of January.

This comet is moving North rapidly: last night it was in Cancer, heading towards Gemini.
I saw that it had risen above the trees soon after 9pm, so I did an imaging run when I'd finished with C/2016 R2.
It was moving so quickly that I had to shorten my exposures to 60-sec to reduce the trailing.
It crossed most of my field of view within 70 minutes, as this animation shows:
http://www.qsl.net/g6gvi/astro/c2017t1_27dec.mp4

Now this comet is tracking very quickly across the sky.
When I caught it last night on the border of Cassiopeia, it was even trailing on 1-min exposures:
The gap in the dotted star-trails is due to a strand of cloud which came over for a couple of minutes.