The end of 2018 could have a wonderful surprise in store for us: a comet visible to the naked eye.
Comets are mountain-sized blocks of ice and rock. As they approach the Sun, these celestial bodies are warmed and fragmented by the solar wind, which creates a diffuse halo called the coma around their nucleus, and two long tails, which are capable of stretching several million kilometers in length.
Some comets get close to the Sun just once, and then return to the outer reaches of the solar system. Other comets, conversely, pass close to the Sun on a regular basis. The most famous of those is Halley’s Comet, which comes back every 76 years. Its next visit is scheduled for 2061.
Features of the 46P/Wirtanen Comet
In the meantime, December will allow us to observe the return of the 46P/Wirtanen Comet. This comet was discovered on January 17, 1948, in a photograph taken at Lick Observatory by astronomer Carl Alvar Wirtanen. The nucleus of the comet is relatively modest, no more than 1.1 kilometers in diameter, compared to 16 kilometers for Halley’s.
The 46P/Wirtanen Comet takes 5.44 years to orbit the Sun. During that orbit it gets as close as 158 million kilometers from the Sun and travels more than 767 million kilometers away from it.
What will we able to see when it visits this year?
This year’s visit may be spectacular, with the comet being no further from us than 11.6 million kilometers on December 16, barely four days after reaching maximum closeness to the Sun. The nucleus should still be active at that point and the comet very brilliant.
Astronomers reckon that the comet could peak at magnitude 3 on that date, meaning bright enough to be observed with the naked eye, which is rare. As the time of writing, the evolution of the comet’s brightness is consistent with predictions. But we have to be cautious, since there are many elements that influence the brightness of comets. Sometimes comets can have a surplus of brightness, either because an area of the nucleus is more active or because that area has fragmented.
The comet will be favorably located in the Northern Hemisphere sky to facilitate observation. It’s heading towards the constellation Taurus; you’ll therefore be able to observe it after sunset on the east side. During the evenings of December 15 and 16 it will be on the left of the Pleiades cluster – a terrific opportunity to admire two of the heavens’ jewels at the same time. On December 23 it will be on the left of the brilliant star Capella in the constellation Auriga.
The comet will appear as a fuzzy smudge in the sky and will be easier to make out through binoculars or with a low-magnification telescope. Comets are rare and difficult to observe, and seeing a bright one is always impressive.
So let’s hope that the 46P/Wirtanen Comet offers us a wonderful celestial gift for the holiday season.