Over the next two months, astronomers predict that we will be entertained by the most spectacular celestial sights mankind has ever seen.
Comet ISON was first identified in September 2012 by a Russian research team working for the International Scientific Optical Network (ISON), whose job was to search for objects in near-Earth space which may pose a threat.
ISON was hard to detect because its trajectory was almost straight in toward Earth, with very little lateral motion to show up on telescope film.
ISON was six astronomical units (AU) away when it was first detected., a bit farther out than Jupiter’s orbit. One AU is the average distance from Earth to the Sun.
ISON has been sneaking in toward Earth from behind the planet Mars, making it difficult to spot, even with a telescope.
On Oct. 31, ISON crossed Mars orbit, 40 million miles from the red planet, and will appear far enough ahead of Mars to be distinguished as a separate object.
ISON will cross Earth orbit on Nov. 1, and loop around the Sun by Nov. 30 to start its travel back toward Earth.
If the Sun’s gravity does not cause ISON to break up (a possibility, but not likely), ISON will pass 48.8-million miles behind Earth in its orbit on Dec. 15 on its way back to the Ort Cloud.
Astronomers say what makes a comet so spectacular, is its brightness and its tail. A large percentage of the comet’s mass is ice, frozen to near absolute zero for millions of years out in the Ort Cloud (an area one light-year across), where trillions of comets rest until disturbed, causing their plunge toward the Sun.
Astronomers believe that this is the first time for ISON to “take the plunge.” Its ice is still intact. Other “periodic” comets have made the trip hundreds of times gradually diminishing the amount of ice that remains. Since 240 B.C., Haleys Comet has been observed making its visit every 76 years, last appearing in 1986.
ISON will pass 730,000 miles from the surface of the Sun, when the surface of ISON will soar to 3,600 degrees F. A lot of ice will evaporate, and dust will be emitted to form the comet’s tail.
The comet’s tail will be pushed away from the Sun by solar winds. The tail will trail the comet inbound, and lead the comet outbound.
The light of the Sun striking the water vapor and dust is what causes the bright light of the comet.
ISON will be visible with the naked eye for much of its passage, longer with binoculars or telescopes. Expect these items to get popular by mid-November with short supplies.
Best viewing is 4 hours before sunrise in the eastern sky starting Nov. 1, trailing to 10 minutes before sunrise on Nov. 29, then expanding to seven hours before sunrise on Dec. 26, after which ISON will always be above the horizon.