Comet ISON's Brightness

Comet ISON

 

The Brightness of Comet ISON on its Discovery Date (September 21, 2012)

At the time of the discovery of Comet ISON, it's apparent magnitude (brightness) was approximately 18.

 

 

Early Predictions for the Brightness of Comet ISON (Late 2012 - Early 2013)

Great Comet of 1680

Great Comet of 1680 (C/1680 V1)

Credit: Painting by Dutch artist Lieve Verschuier (1680)

Comet ISON (C/2012 S1) had a chance to be one of the brightest comets in history, rivaling the Great Comet of 1680 (C/1680 V1) or Comet Ikeya-Seki (C/1965 S1), which reached an apparent magnitude of -10 in 1966. According to The Minor Planet Center, ISON it could reach an apparent magnitude of -9, if it survived its perihelion. Other estimates, on the high end, ranged between -11 and -16. For reference, the full Moon has an apparent magnitude of -12.6. If Comet ISON (C/2011 S1) could reach an apparent magnitude of only -5.6, it would sit alone atop the list of the brightest comets in the 21st century, a position currently held by a comet that dazzled spectators in the southern hemisphere in January of 2007 - Comet McNaught (C/2006 P1).

 

1,817 observations of Comet ISON were used to create a light curve. The resulting graph showed that ISON is increasing in brightness relatively quickly as it travels through the inner solar system. If this increase continues, some astronomers suggest Comet ISON could be much brighter than -9, even brighter than the full moon. However, other comets from the Oort Cloud have been promoted as a spectacular naked eye comet, then fizzled.

 

Ikeya-Seki Comet
This photo of Ikeya-Seki was taken in 1966. Credit: © Roger Lynds/NOAO/AURA/NSF

Raminder Singh Samra, of the H.R. MacMillan Space Centre in Vancouver, Canada is more cautious than most, "While some predictions suggest it [Comet ISON] may become as bright as the full moon, and even visible during the day, one should be cautious when predicting how exciting a comet may get.” Noted astronomer, David Levy, once famously echoed this caution by stating, “Comets are like cats. They both have tails—and they do exactly what they want.” We’ll all simply have to wait and see, but 2013 has a chance to be an incredible one for comet-watchers. The path of Comet ISON will take it within 40,000,000 miles (64,000,000 km) of Earth.

 

In mid-November it should brighten for a couple weeks before it disappears into the evening twilight.

 

On November 28, 2013 it will reach its closest point to the Sun--at roughly 724,000 miles (1.2 million km). This is roughly 16 times closer than Mercury. Will Comet ISON survive the 4,900 degrees Fahrenheit (2,700 degrees Celsius) at this distance, the Sun's intense gravity, and solar radiation? It's anyone's guess. If it can, it has a chance to become the most spectacular comet any of us will see in our lifetime.

 

Kaustuv Chaudhuri, secretary general of Kolkata Astronomy Centre, says that even if the comet fragments into two or more pieces, "...you can still get a spectacular view because...it would appear as a string of pearls,” Chaudhuri says, "...the comet [will] be at its maximum brightness during late November, it [will] appear in the day sky very close to the Sun making sightings not only difficult,but dangerous. People should not see it with binoculars, X-ray plates, dark glasses because it would cause damage to eyes."

 

Many are optimistic Comet ISON will become the "Comet of the Century", when it separates enough from the Sun to be seen with the naked eye before sunrise in early December.

 

 

 

Comets from the Oort Cloud (June 2013)

Universe Today interviewed John Bortle, a comet hunter and observer. He said the following concerning ISON's possible apparent magnitude in late 2013.

 

“Comets coming into the near-solar neighborhood from the Oort Cloud for the very first time tend to behave rather differently from most of their other icy brethren. They often will show considerable early activity while still far from the Sun, giving a false sense of their significance. Only when they have ventured to within about 1.5-2.0 astronomical units of the Sun do they begin to reveal their true intrinsic nature in the way of brightness and development. When discovered far from the Sun, this situation has misled astronomers time and again into announcing that a grandiose display is in the offing, only to have the comet ultimately turn out to be a general disappointment. There have been exception to this, but they are rare indeed.”

 

 

Comet ISON crossing the "Frost Line" (July 19, 2013)

Jian-Yang Li, a research scientist with the Planetary Science Institute, says that Comet ISON is crossing the "frost line." This is an area in space between Mars and Earth where the nuclei of comet really start to heat up and shed material. That's when and where, "we get this beautiful tail on a comet, and the coma, and all that stuff starts to appear." Astronomers can get a better idea regarding the potential brightness of Comet ISON.

 

 

 

Has Comet ISON Fizzled? (July 30, 2013)

Ignacio Ferrin, an astronomer with the University of Antioquia in Colombia claimed, "The future of Comet ISON does not look bright...Comet ISON has been on a standstill for more than 132 days."

 

Ferrin's calculations show that the comet has not brightened since mid-January, which is puzzling. Some possible reasons for this have been discussed. One, it could indicate that Comet ISON (C/2012 S1) is already out of material that could evaporate from the comet to form and coma and tail. This is highly unlikely. Two, it could indicate that the comet is covered by a layer of material that is preventing the nucleus from shedding water and other materials. These materials are, of course, heating up the closer Comet ISON gets to the Sun--currently at a speed of 16 miles per second (26 kilometers per second).

 

Comet ISON's tail is currently long enough to wrap around the Earth seven times.

 

 

Comet ISON versus The Sun. The Sun Wins. (Nov. 28-29, 2013)

Unfortunately, the nucleus did not survive its close encounter with the Sun. It was declared dead by the European Space Agency on November 28, 2013. A small piece of the comet "came back to life" on November 29 and was detected by STEREO-A and the Solar Heliospheric Observatory (SOHO). However, it faded quickly and the remnants were invisible to the naked-eye after sunset. Although Comet ISON disappointed the general public, the coordinated study of Comet ISON by multiple space agencies and astronomers was incredible. The data gathered will advance our understanding of comets.

 

 

 

 

 

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