Stars over Sisters

Stargazers around the world were delighted by the appearance of two relatively bright comets earlier this year. Comet PANSTARRS approached to within 28 million miles of the sun on March 10, while comet Lemmon came nearest the sun on March 24 at a distance of 68 million miles.

Though just a shade too dim to be seen by the naked eye, local amateur astronomers, using binoculars and telescopes, shared their views of these objects with interested spectators at public viewing sessions. But there is a third comet on its way to the inner solar system that has the potential to greatly outshine the previous two.

Comet C/2012 S1 ISON was discovered on September 12, 2012, by two Russian astronomers using a 16-inch telescope that is part of the International Scientific Optical Network (thus the name ISON) located near Kislovodsk, Russia.

Comet ISON will reach its closest point to the sun (perihelion) on November 28, 2013. At that time the comet will be only 680,000 miles above the surface of the sun and will be only one degree from the sun as seen from the earth, making it very difficult to see. The temperature at perihelion will be 4,890 degrees Fahrenheit, which is hot enough to melt iron.

ISON is a new comet that is making its first appearance in the inner solar system. The comet is from the Oort Cloud, a huge sphere of material left over from the formation of the solar system, that surrounds the sun and extends out about one light-year from the sun.

Originally researchers speculated that ISON might become very bright, but based on more recent observations, it may be too faint to see with the naked eye although it may be seen in binoculars. In comparison, the brightest comet since 1935 was Comet Ikeya-Seki in 1965, which was magnitude 10, far brighter than the planet Venus.

There have been many exceedingly bright comets, called "Great Comets," throughout history. Twenty-one of these appearances involved Halley's Comet.

One of the earliest great comets was Caesar's Comet of 44 BCE. This was the most famous comet of antiquity. The seven-day visitation was taken by Romans as a sign of the deification of the recently dead dictator, Julius Caesar who died that year.

The great comet of 1556 had a diameter half the size of the moon as seen from the earth.

The comet of 1680 was bright enough to be seen in daylight and was the first comet discovered with a telescope. It was noted for its spectacularly long tail.

Donati's Comet of 1858 was the brightest comet of the 19th century and was seen by Abraham Lincoln. It was the first comet to be photographed.

The great comet of 1910 was the brightest comet of the twentieth century. It is sometimes called the Great Daylight Comet. When it was discovered it was already bright enough to see with the naked eye. It had a noticeably curved tail that reached a length of 50 degrees. That same year Halley's Comet returned.

Comet Ikeya-Seki was the great comet in 1965. This correspondent remembers seeing Ikeya-Seki close to the sun in daylight. The comet broke up into three pieces when it passed close to the Sun. A similar fate may await ISON.

Then in back-to-back years of 1996 and 1997, two springtime comets lit up the night sky. Comet Hyakutake came first and sported the longest tail of any comet ever seen, passing very close to the earth. A year later Hale-Bopp burst on the scene. This comet never got close to the earth, but it was very large and could be seen with the naked eye for 18 months!

There have been many extravagant claims made regarding ISON. Some say it will be as bright as the full moon! Remember Comet Kohoutek from 1973? Before its close approach, Kohoutek was hyped by the media as the "comet of the century." Because Comet Kohoutek fell far short of expectations, its name became synonymous with spectacular duds. Like ISON, it was a long-period comet from the Oort Cloud making its first appearance to the inner solar system. Traditionally new comets from the Oort Cloud under-perform during their maiden voyage toward the sun. Already ISON has not brightened as much as astronomers thought it would.

NASA is now saying that because comet ISON is not brightening as predicted that it probably will NOT be visible to the naked eye, but will be bright enough to be seen with binoculars. No comet of the century. However, as the famous comet observer John Bortle has said, "Comets are like cats, they have tails and do exactly what they want to do." Who knows? Maybe when ISON gets closer to the sun it will brighten unexpectedly and surprise

everyone.

Despite the underperformance of comet PANSTARRS last spring, and disappointing progress of ISON so far this fall, 2013 may still deserve the title "Year of the Comet."

The Sisters Astronomy Club (SAC) is currently observing six other comets that can only be seen through binoculars or a modest-size telecope. It is unusual to be able to see that many comets in the sky at the same time. These comets include 154P/Brewington, C/2013 R1 (Lovejoy), 2P/Encke, C/2012 X1 (Linear), C/2013 N4 (Borisov), and C/2010 S1 (Linear).

For updated information about comet ISON, visit SAC's home page at www.sistersastronomyclub.org.