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A Bright Green ‘Christmas Comet’ Will Fly the Closest to Earth in Centuries

The comet 46P/Wirtanen as seen from France through a telescope this month.Credit...Nicolas Biver/Agence France-Presse — Getty Images

Look into the night sky on Sunday and you just might see a bright, fuzzy ball with a greenish-gray tint.

That’s because a comet that orbits between Jupiter and the sun will make its closest approach to Earth in centuries, right on the heels of this year’s most stunning meteor shower.

“The fuzziness is just because it’s a ball of gas basically,” Tony Farnham, a research scientist in the astronomy department at the University of Maryland, said on Saturday morning after a long night studying the comet at the Discovery Channel Telescope, about 40 miles southeast of Flagstaff, Ariz. “You’ve got a one-kilometer solid nucleus in the middle, and gas is going out hundreds of thousands of miles.”

The comet glows green because the gases emit light in green wavelengths.

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The ball of gas and dust, sometimes referred to as the “Christmas comet,” was named 46P/Wirtanen, after the astronomer Carl Wirtanen, who discovered it in 1948. It orbits the sun once every 5.4 years, passing by Earth approximately every 11 years, but its distance varies and it is rarely this close. As the comet passes by, it will be 30 times farther from Earth than the moon, NASA said.

[Read about 2019’s interstellar ‘Christmas comet.’]

The proximity of 46P/Wirtanen provides an opportunity to research the tail of the comet and see farther into the nucleus.

“The fact that it’s brighter means we can study a lot of different gas types that we normally can’t study because they’re too faint,” Dr. Farnham said, adding that researchers could learn more about where the comet formed and how it evolved.

The comet is also interesting to scientists because it is hyperactive, meaning it emits more water than expected, a phenomenon that is relatively rare.

Dr. Farnham oversees an online clearinghouse of information about the comet that educates the public and encourages collaboration among astronomers who gather data about it.

The comet is visible now but it will shine even brighter on Sunday as it reaches its closest approach, 7.1 million miles from Earth. That may sound really far, but it is among the 10 closest approaches by a comet in 70 years, NASA said. Only a few of those could be seen with the naked eye.

Don’t worry if you miss the comet on Sunday. It should be just as visible for a week or two because its appearance will change gradually. People “can try to find it a few days later without it being too much different,” Dr. Farnham said.

After it moves on, it won’t be this close to Earth again for hundreds, if not thousands, of years, he added.

Those who live in areas with low levels of light pollution will most likely be able to see the comet with the naked eye. People who live in cities may need binoculars or a telescope to get a glimpse. Online charts can help pinpoint its location.

If you would rather not venture outside, try a graphical simulation of the comet on your computer, phone or tablet by using free planetarium software like Stellarium or KStars. For a closer look, amateur photographs of the comet are continually being uploaded at websites like Comet and Asteroids Collaborative Astronomy Observers and Space Weather.

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