Great Outdoors

A comet brightens the holiday sky over Northern New Mexico

By Gary Zientara
Mount Sangre Observatory
Posted 12/26/18

Comet Wirtanen may be one of those rare comets visible to the naked eye.

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Great Outdoors

A comet brightens the holiday sky over Northern New Mexico

Posted

Each year, dozens of comets come close enough to Earth to be detected by telescopes.

A few can be seen through binoculars. But rarely any can be seen using just your own eyes.

Comet Wirtanen (WERE-tan-EN) may be one of those rare comets visible to the naked eye. As of the beginning of Thanksgiving week, Comet Wirtanen has brightened to magnitude 5, still too dim to see without binoculars. But this comet continues to get closer to the Earth and to the Sun at the same time. Its closest approach to us (about 7 million miles) coincides with its closest approach to the sun (perihelion).

This virtually assures that this comet will shine at least five times brighter than it does now. That dramatic brightening began on Dec. 1 and reached its maximum Dec. 16. Right now, the full moon's glare may wash out the much dimmer comet.

The nucleus of Comet Wirtanen is only .75 miles in diameter. However, it is composed of lots of dirty snowy ice and volatile gasses that, when heated by the sun, will form a fog (coma) around it, extending thousands of miles from its surface. Included in the coma is C2 or diatomic carbon, which glows green when exposed to sunlight.

Some "experts" say that the green glow is from CN or cyanogen gas, but CN glows purple when exposed to the sun's radiation. I intend to take the spectrum of Comet Wirtanen using the diffraction gradient filter on the Mount Sangre Observatory telescope to detect the gasses in Wirtanen's coma. I hope to publish the results in the January 2019 issue of the Universe from Mount Sangre Observatory mountsangreobservatory.com.

Comet Wirtanen (catalogued as 46P/Wirtanen) is a short-period comet discovered in 1948. It orbits the sun once every 5.4 years. It belongs to a family of comets that have had their orbits drastically changed by the gravitational influence of planet Jupiter.

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