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Martin Mobberley has released a new image of the comet 46P / Wirtanen taken remotely from Siding Spring in Australia on October 27, 2018. This image shows a large coma – or cloud around the comet – usually seen when comets approach of the sun. Image via comets and asteroids on Facebook.
Have you heard of Comet 46P / Wirtanen? The planet Wirtanen is the brightest comet in the night sky, although that does not mean you can only see it with your eyes. In fact, it is visible only for astronomers equipped with telescopes. But in December 2018, Comet Wirtanen could be visible to the naked eye, at least in dark skies. The closest approach to the sun will be December 12, 2018 and the closest approach to Earth a few days later, December 16.
According to astronomers from the University of Maryland, this passage of comet Wirtanen near the Earth (that is to say, up to the standards of the comet) will be the tenth closest approach to the comet of modern times . At its closest, the comet will have about 30 times the distance of the moon (7.1 million miles, or 11.5 million km).
Compare this figure to another comet that recently swept us relatively close – 21P / Giacobini-Zinner, which caused a brief explosion of Draconid meteor shower this year – and swept the closest to Earth on September 9th and 10th 2018 to 36 million miles million km). It was the closest Giacobini-Zinner had come in 72 years!
And you can see – according to the above paragraphs – that Wirtanen is getting very close, though several times farther from the moon.
This is called a light curve. It is a measure of the brightness of the comet 46P / Wirtanen, over time. The comet becomes brighter! In December, it may be bright enough that you can watch it only from a dark place. Image via the University of Maryland comet 46P / Wirtanen: current state page.
Estimates indicate that Wirtanen could reach a visual magnitude of 3.5 to 6. This would clearly place the comet in the field of visibility to the naked eye (although diffuse objects, such as comets, are more difficult to see that the landmarks of stars of comparable magnitude).
And, of course, it has been shown that comets are unpredictable. We will keep you posted.
Want to stay informed about the brightness of Wirtanen? This Web page of the University of Maryland provides updates.
Comet Wirtanen's close approach on December 16, 2018 will take place less than 4 days after the comet's perihelion, or the closest point of the sun. As comets become more active as they get closer to the sun that connects them to orbit, we can expect this comet to be close to its maximum brightness. It may be visible to the eye from a dark place. Image via the University of Maryland.
In summary: comet Wirtanen will approach Earth in December. At this point, it may be visible only to the eye.
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