Comet here for Christmas
December 11th 2018
This month we get a chance to see the brightest comet of 2018. Unfortunately that's neither as exciting nor as easy as it sounds because most comets are too faint to see at all and this one, "Comet 46P/Wirtanen", is barely bright enough to be visible to the naked eye.
The popular image of a comet includes a large nucleus (head) and long tail. Being able to see a comet like this is relatively rare and there have only been a few so far this century. Most comets appear as faint, fuzzy spots with no obvious tail. That's the best you can hope for with 46P.
Comets are small, icy objects that are spread throughout the Solar System. Their orbits occasionally bring them into the vicinity of the inner planets and Sun, where the increased heat causes them to release tails of dust and gas. Comet 46P does currently have a tail but it requires a good telescope to see.
46P/Wirtanen was discovered in 1948. It is estimated to be around 1.5 km in diameter and it passes near Earth about every five and a half years. This year it will pass within 12 million km of us on December 16.
The sky chart below shows how much this comet moves each night. It's in an area of the sky we've talked about before, on a course between Matariki and the Hyades. Use the chart to see roughly where it will be on any night this week. The inset shows what you can expect to see.
The sooner you can see it the better. The Moon is getting closer and brighter each night, making it much harder to see the faint comet. It also helps a lot to get away from the lights of towns and cities.
If you're keen to magnify the comet, a pair of binoculars might be the best bet because they provide a wide enough field of view to fit the whole thing in comfortably. Of course if you have access to a telescope, you'll want to try that too.
Below: This column as it appeared in the Wāipa Post (click for full-sized version)