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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.

September 2013 night sky

—Charlie Christmann

Fire in the sky

Novae (yes, that is the plural of nova) occur frequently throughout the universe, but it is not often that one can be seen with the naked eye, briefly blazing where no star was visible before. On August 14, a supernova burst into the night sky and was visible for several nights before fading back into obscurity. Supernova Delphinus 2013 peaked at about magnitude 4, visible under dark skies away from city lights and easy to see with binoculars if you know where to look. Unfortunately, as you read this article, the supernova will probably have faded into the background.

If you want to try your luck and have a telescope, SN Delphinus 2013 is located in the edge of the constellation Delphinus, the Dolphin, roughly five degrees above the diamondhead of the constellation (your clenched fist held at arm’s length is about ten degrees). To the east of Delphinus is the small, dim constellation of Sagitta, the Arrow. It just happens that the arrowhead of this star pattern points almost directly at the nova. At 9:30 p.m., Delphinus rides high in the southeastern sky.

Supernovae are former stars that have blown themselves up, briefly outshining their home galaxy. A supernova explosion can result from two different types of events. The first is from a heavy star—weighing more than eight times the mass of our sun—that exhausts the fuel needed to run its internal fusion engine. As the star collapses, the core compresses and heats up, exploding as a Type II Nova. These novae are the universe’s only source of elements heavier than iron. The result of this type of event is either a weird object called a neutron star, or an even stranger object called a black hole.

The other supernova form is called a Type I Nova. This type occurs in a multiple star system where a white dwarf star steals matter from its partner. After enough of the stolen material piles up on the dwarf’s surface, it explodes like many huge nuclear bombs. Astronomers use a subset of Type I Supernovae as “standard candles” to measure cosmic distances. Theory says that Type I novae all shine with the same absolute brightness and the apparent brightness can be used to estimate distances.

On average, a supernova will occur about once every fifty years in a galaxy the size of the Milky Way. Yet, with billions of observable galaxies, a star explodes almost every second somewhere in the universe.

Comet ISON

In September of last year, amateur astronomers Vitali Nevski and Artyom Novichonok spotted a comet in photographs taken by a telescope in the International Scientific Optical Network (ISON). After computing its orbit, astronomers discovered this would be a “sungrazer,” meaning it would pass very close to the sun in November 2013.

On November 28, 2013, comet ISON is expected to pass eighty thousand miles from the sun’s surface, exciting scientists with the possibility of a bright comet visible with the naked eye in December. Some even predicted it could be bright enough to be observed in daylight—assuming the comet survives its close encounter with the sun.

The enthusiasm for this comet is predicated on the similarity with the Great Comet of 1680. “That comet put on a dazzling show; it was glimpsed in daylight and later, as it moved away from the sun, it threw off a brilliantly long tail that stretched up from the western twilight sky after sunset like a narrow searchlight beam for some seventy degrees of arc,” according to columnist Joe Rao in a September 2012 article.

However, new observations may be throwing cold water on the ISON show. As of mid-August, the comet reappeared from behind the glare of the sun and was just outside the orbit of Mars where the sun’s heat can start to vaporize any of its water. August observations show a dimmer than expected comet prompting predictions of a “fizzle.” However, most astronomers say it is still too soon to predict the fate of ISON.

On October 1, ISON will pass close to Mars. NASA is hoping to use the Mars Reconnaissance Orbiter to observe and study the comet. Perhaps those observations will help predict if the comet will put on a spectacular show or be a disappointing dud.

Friday the 13

September has the first of two Friday-the-Thirteenths in 2013. The next occurs in December, exactly thirteen weeks later.

Last year had three Friday-the-Thirteenths, all thirteen weeks apart (January, April, and July). 2007 also had two Friday-the-Thirteenths thirteen weeks apart.

Interestingly, since the start of the Gregorian calendar in 1582, the thirteenth day of the month has fallen on Sunday 687 times, Monday 685 times, Tuesday 685 times, Wednesday 687 times, Thursday 684 times, Friday 688 times, and Saturday 684 times.

Night Sky

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