In Alaska, we're accustomed to ice in many forms. Ice in brilliant shades of blue and silver. Calving ice, polar ice, glistening ice in the merest crystals of snow. But this month, we're in for a very rare treat. Comet ISON is blazing through the inner Solar System toward the sun with a trail of dust and gas from an ice of long ago. From the edges of distant space, its exhilarating million-mile journey has been putting on a spectacular show for amateur sky-watchers and scientists alike.
On Thanksgiving, ISON will make its brush closest to the sun, bringing it within 730,000 miles of its surface. With the fierce gravitational pull, ISON increases in speed. At the beginning of November, it was clocked around 95,000 mph and will reach an estimated 845,000 mph at its peak. If it survives the blistering pass and does not fragment, it will cross into the northern sky Dec. 8. In just a few more days, we'll know its fate.
Discovered in 2012 by Russian amateur astronomers, Comet ISON was recorded at a bright 19th magnitude. Officially designated C/2012 SI, ISON is named after the International Space Optical Network. Current updates and images are available at NASA's ISON Comet Observing Campaign.
Various NASA spacecraft and viewers around the globe are watching its fate closely, including those from the Keck Observatory on the Big Island of Hawaii. "We're preparing for it with a number of observers," said Greg Wirth, a support astronomer at Keck. "We're excited to see what happens."
What is a comet?
Comets are solid bodies in space. Some relics come from the Solar System's beginnings, some 5 billion years ago. They're sometimes referred to as dirty snowballs and contain dust and frozen gases including ammonia, methane and carbon dioxide. Their tails can span great distances, elongating as they travel.
Like most comets, ISON originates from the Oort cloud, a massive spherical cloud of trillions of icy bodies. "The Oort cloud defines the edge of the solar system, some 50,000 au away," said Wirth. Since one astronomical unit (au) equals 93 million miles from the sun, that's pretty far. Dutch astronomer Jan Oort hypothesized the region in 1950.
Some researchers think comets may have originally brought some of the organic molecules to Earth that helped create life here. "These visitors bring with them what was out there when the solar system formed," said Wirth. They may be able to tell us the composition of materials on the planet at the origin of Earth's water and life.
"The elementary building blocks of life may have come from them," Wirth said.
Comet ISON is a sun-grazing comet, one that comes dangerously close to the sun. It appears bright due to the sun's light. It heats the comet's solid part, the nucleus, turning the ice into gas. The gas in turn spews and trails with dust and rock debris, releasing a torrent that can stretch hundreds of millions of miles.
Comets through history
In ancient times, comets were sometimes seen as portents of disaster or great historical change. They symbolized such things as omens or messengers of the gods -- sometimes inspiring dread, fear, and awe. Comets were among the most remarkable objects in the night sky.
"Throughout history, the stars are unchanging," said Wirth.
"For ancient cultures, it was their calendar. The sky was predictable. There were only a few things in the sky that did change. Comets would seemingly appear out of nowhere. They were the only thing that would surprise you. For millennia, people have been looking at them with wonder and curiosity," Wirth said.
Since comets appear so rarely, many people are lucky to experience one in their lifetime. Comet Hale-Bopp, perhaps the most observed of the 20th century, was one of the brightest in 1997. The more famous Halley's Comet, a periodic comet, returns to Earth's vicinity around every 76 years. It was named after English astronomer, Edmond Halley, (1656-1742). Earliest accounts of its sightings date to 466 BC by Chinese astronomers. Babylonian tablets as well as the ancient Greeks and Romans, also documented it.
Halley's apparitions have coincided with major events throughout history. One of its most famous appearances occurred shortly before the 1066 Battle of Hastings. An artwork depicting the event, Britain's Bayeux Tapestry in France, chronicles the Norman invasion of England with Halley's comet as a fiery star in the landscape. The comet's 1301 apparition may have also inspired Giotto's frescoe, the "Adoration of the Magi," in which the comet shines gloriously overhead.
Then there was Halley's notable 1910 apparition. In his 1909 autobiography, Mark Twain said, "I came with Halley's comet in 1835. It will be the greatest disappointment of my life if I don't go out with Halley's Comet." He died shortly after the comet's return. Halley's last show was 1986, and it won't return until 2061.
"Comets are important," said Wirth. "They carry the seeds of life throughout the galaxy."
Viewing Ison
According to Astronomy.com, the comet "will peak on Thursday around magnitude -6.7, making it much brighter than Venus," as predicted via the Minor Planet Center at the Harvard-Smithsonian Center for Astrophysics. Astronomy.com says "its much better to wait until ISON re-emerges on the other side of the Sun two or three days later." Extensive maps and guidance on observing the comet are available here. Updates and video are also available here.
Backyard viewing tips
If ISON survives, it will likely be visible with the naked eye come December. Comets are spectacular draped against a night sky. Here's some tips for backyard viewing:
• Use proper filters and safety precautions with all observing gear, including cameras.
• A pair of good astronomy binoculars is ideal. Wide field view is a must. Some 10x50s, 15x70s, 20x80s or giant binoculars, say 25x100, should do the trick.
• Light pollution filters are also useful.
Proper shielding and safety are a must for any celestial viewing. Do not attempt to observe or photograph Comet ISON when it is close to the sun or at perihelion. Staring directly at the sun, especially through a camera, telescope or binoculars without a proper, safe filter, can result in serious eye injury.
Tracey Pilch is an amateur astronomer and adjunct professor at Alaska Pacific University.