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  Night Sky

Enjoy the starry night skies
Be a considerate neighbor. Reduce nighttime glare. Shield your outside lights downward. Let the stars light up the night.

November 2013 night sky

—Charlie Christmann

Sizzle or fizzle?

Now inside the orbit of Mars, Comet ISON has been spotted in the morning sky by amateur telescopes. It is still at very dim magnitude of ten (7th magnitude is about as dim as a human can see in our sky; larger magnitude numbers are dimmer). Since its discovery in September of 2012, C/2012 S1 ISON’s billing as the “Comet of the Century” has raised hopes of an early December spectacle.

Comets are loose collections of rubble, which include lots of ice and other volatile materials left over from the original formation of our solar system some 4.5 billion years ago. Billions of similar icy bodies may reside in a region surrounding the solar system, called the Oort cloud, almost a light-year from our sun. Instability, gravitational disturbances, and collisions occasionally send a few of these planetesimals careening toward the sun. ISON is one of these wayward comets. If it survives this trip around the sun, it will be ejected from our solar system around 2050, never to return.

The big question that must be answered before this comet puts on any show is, will it survive its encounter with the sun? As a comet nears the sun, the ices begin to melt and vaporize. The outgassing also throws out dust and other comet materials from the surface causing the coma (head) of the comet. The sun’s solar wind sweeps material away from the head forming a tail of dust and gas pointing away from the sun. The gas pressure and thermal stresses tend to fracture comets.

If ISON falls apart before rounding the sun, the show will be canceled. At its closest approach on November 28, ISON will be less than three quarters of a million miles above the boiling surface of our star. Most comets do not survive encounters farther away than that. But, it is this extremely close pass that has scientists excited. Being that close to the sun will really boil off gasses and dust, potentially making ISON very bright in the evening sky in early December. Some even predict it may be visible in the daylight.

According to photos taken on October 9 by the Hubble Telescope, ISON is still healthy, sporting a greenish tail composed of cyanogen (CN) and diatomic carbon (C2). Astronomers estimate that ISON may be visible with the naked eye under darks skies by Halloween. After December 8, ISON will be in the northern sky after sunset, rising higher each night as Christmas approaches.

For those looking through telescopes, ISON is crossing from Leo into Virgo to start November. On November 18, look near the star Spica.

Comet Family

ISON is not the only comet in the inner solar system now. There are two other morning comets joining in the fun this November. C/2013 R1 Lovejoy, discovered just last month, will make its closest approach to the sun on Christmas day. Lovejoy can be found with a good telescope around Mars the first part of November.

Comet 2P/Encke is also lurking in the morning sky. This is a periodic comet circling the sun every three years. Comet Encke is thought to be the cause of several related meteor showers known as the Taurids, which are seen as the Northern Taurids in November, and the Beta Taurids in late June and early July.

All three are expected to be marginally visible to the naked eye late this month.

Threats from Above

I have talked about Apophis, the asteroid that will make a close approach to Earth in April 2029 and an even closer approach in April 2036. This is just one of more than 1400 potentially hazardous asteroids being tracked by NASA. One more has been added to the total with asteroid 2013 TV135. It streaked by Earth on September 16, 2013 at a distance of about four million miles. We will have another very close encounter with 2013 TV135 on August 26, 2032. Current estimates of a collision give us a one in 14,000 chance of disaster. Should this 1300 feet wide chunk of rock impact the Earth, it would explode like 2,400 megatons of TNT, fifty times the energy of the largest hydrogen bomb ever detonated.

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