Your Sky Tonight A Christmas Comet

In the waning months of 2018, we are treated to a comet in our night sky: Comet 46P/Wirtanen

Published on 22nd Dec, 2018

In the waning months of 2018, looking up in the eastern, early evening sky in the northern hemisphere, we are provided with a celestial Yuletide present. Moving just above the constellation Taurus the Bull throughout the winter solstice period, lies a Christmas comet. Because of the glare of the waxing Moon, it will require a small pair of binoculars to see, but scanning the skies just above the bright star cluster of the Hyades, you’ll come across a dim, greenish patch of light: a small, short period comet known as 46P/Wirtanen. Here is what it looks like in high-end amateur telescopes. These images were taken by amateur astronomer Alexander Reinders. By taking 72 images of 30 second exposures each and adding them all together, the green haze of the comet can be seen. The star trails are due to the telescope following the comet and centering it in the frame as it travels towards the Sun, causing the background stars to create tracks in the image. Here is a wider field view from a Canon DSLR with a 200mm lens following the background stars instead of the comet. 72 images were taken at 30 second exposures to make this movie. Discovered in 1948 by Carl Wirtanen, it orbits the Sun once every five and a half years is 1.2 kilometers in diameter and was considered as a landing site by at least two space agency comet missions. Tonight, during this 2018 Christmas season, comet 46p/Wirtanen is making its closest approach in 20 years, making this pass one of its brightest. At magnitude 4.2 it could be seen by the naked eye under dark sky conditions, but the waxing moon makes this very difficult so a pair of binoculars or a small telescope will help viewing. The relatively uncommon greenish hue seen is due to gaseous cyanogen surrounding the rocky core of the comet itself. As comets approach the Sun and heat up, the cold, frozen elements on the comet’s surface sublimate or turn into a gas, which in this case, creates a christmassy green cloud that envelopes the comet’s rocky mass. Comets were long thought to be harbingers of bad tidings, we now know these periodic visitors are remnants of our early solar system, leftovers from planet formation so now when we see them, especially during the winter solstice they can bring tidings of both comfort and joy.