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Brightest comet of the year slowly approaches

CBC News

Saturday, December 8, 2018, 3:50 PM - If you have clear skies and are willing to brave the chilly temperatures, you might want to head to a dark site and look for a passing visitor.

Comet 46P/Wirtanen, first discovered in 1948, will have its closest encounter with Earth on Dec.16. But it's already visible in the sky.

While this is the brightest comet of the year and the 10th closest comet in modern times, don't expect one with a well-defined tail, a hallmark of comets.

At the moment, Wirtanen — a small comet at just 1.2 kilometres in diameter — is a fuzzy, bluish object in the southern sky. Recent photos do show a thin tail, but nothing very pronounced. Wirtanen will likely brighten as it makes its closest approach to the sun on Dec. 12.

Malcolm Park captured this image of comet 46P/Wirtanen from Prince Edward County, Ont., on the night of Dec. 5. (Malcolm Park)

Comets, often referred to as "dirty snowballs," are leftover collections of dust, gas and ice from the formation of our solar system. Most are from two regions — the Kuiper Belt and the Oort Cloud — at the outer edge of our solar system. Once in a while they get knocked out of these regions and begin a voyage around the sun.

As a comet approaches the sun, its ice sublimates (changes directly from a solid to a gas, skipping the liquid phase), which produces its characteristic tail. A comet's brightness depends on its size and how much ice and gas it contains.


The brightness of celestial objects is on a scale that goes from the very brightest — the sun — to the dimmest. And it doesn't go in the direction you'd think: the lower the number (negative values) the brighter the object.

At the moment, 46P/Wirtanen is near magnitude 4, so not quite visible to the naked eye in light-polluted skies. It's estimated that when Wirtanen is at its closest position to Earth, on Dec. 16, it should reach a magnitude of 3.

So, if you're heading out to catch a glimpse of the comet, make sure you try to get to as dark a location as possible. And don't look at your phone. Allow your eyes to adjust to the darkness, which in turn allows you to see dimmer objects.

If you have a pair of binoculars, use them.

Look to the southern sky, where you'll find the very recognizable constellation Orion, known as the hunter. On Dec. 8, Wirtanen will be about 32 degrees to the right of Rigel, the brightest star in Orion's "foot." You can use your fingers to measure the distance.

What you're likely to see, should you find it, is a fuzzy, bluish circle. Over the next week, the comet will continue to rise higher in the sky. On Dec. 16, it will be near the Pleiades, a cluster of stars visible to the naked eye.

The downside is that the moon will be 65 per cent illuminated on Dec. 16, making it difficult to see Wirtanen. However, it will set around 1 a.m., so perfect for night owls hoping to get a glimpse.

A map of where you can find comet 46P/Wirtanen when it's closest to Earth. (CBC News)

Article by Nicole Mortillaro, originally published on CBC.ca


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