Comet NEOWISE.jpg

The two tails of comet NEOWISE. (Image courtesy NASA/Johns Hopkins APL/Naval Research Lab/Parker Solar Probe/Guillermo Stenborg)

Now is your chance to see the brightest comet visible in the northern hemisphere in decades.

Comet C/2020 F3 (NEOWISE), comet NEOWISE for short, is now visible in Kentucky. The comet gets its name from the NASA space telescope that discovered it — the Near-Earth Object Wide-Field Infrared Survey Explorer.

NASA loves acronyms.

The comet is on a 6,800 year-long orbit which takes it as far as 33 billion miles away. Comet NEOWISE just passed its closest point to the sun, called perihelion, on July 3 when it came within 28 million miles of the sun. It will make its closest approach to Earth, called perigee, on July 22 when it is about 64 million miles away, or 2/3 of the average distance from the Earth to the sun.

It’s said that comets are like cats — they both have tails and are unpredictable. Comets rarely live up to expectations, and most of them break up as they approach the sun. We have had several disappointing comets already this year, so having a bright comet that has survived perihelion is very exciting.

The radiation and heat that a comet is subjected to as it approaches the sun is the reason comets disintegrate, and why they have tails.

Comets have two tails. The dust tail is created from material being shed from the surface of the comet due to solar heating and trailing behind the comet in its orbit. This is the most easily visible tail.

The other, less obvious tail is called the ion tail. This tail is formed by gases that have been ionized by radiation from the sun and always points directly away from the sun.

These icy visitors from the edge of our solar system formed 4.6 billion years ago and are composed of rock, water ice, dust and a variety of other elements. We can see from its yellowish dust tail that Comet NEOWISE is particularly high in sodium content. We can also tell from infrared observations that the nucleus, or head, of the comet is about 3 miles across.

In comparison, the dust tail is over 10 million miles long.

Go out and see this comet now. It is visible to the unaided eye from a dark sky site without much light pollution. It is visible with binoculars or a telescope from just about anywhere.

The weekly roundup: The morning sky

Venus rises in the east around 4 a.m. and forms a nice pair with the waning (getting smaller) crescent moon on the morning of the 17th. Mars, rising just after midnight, is high in the south-east before dawn.

The evening sky

Comet NEOWISE is visible in the north west about an hour after sunset. It climbs higher in the evening sky every night as it moves away from the sun. Use an astronomy app or a finder chart online to locate it. Saturn reaches opposition on the 20th. Opposition is the point in a planets orbit when it is on the opposite side of the Earth from the sun. Jupiter and Saturn rise right around nightfall and are visible all night long. 

Dan Price is a NASA/JPL Solar System Ambassador and informal educator. Join him on the 20th for a Moon Day Zoom presentation. Visit the Shelby County Public Library website to reserve your spot. He also leads the Night Sky Tours at Josephine Sculpture Park. Have a question about astronomy or space science? Send an email to dan@starpointestudio.com and it might be featured in a future column.

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