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Even those who are not early risers might consider braving a cold morning just once over the next several months to catch Comet Catalina.

Discovered two years ago in late October by the Catalina Sky Survey based at the University of Arizona-Tucson, Comet Catalina is traveling close to Earth (about 67 million miles at its closest pass) and becoming visible in the east before sunrise. For now, binoculars or a telescope are best for viewing, especially in Evanston where the skies are not very dark. It is not big and bright like Hale-Bopp, seen in 1997, but naked-eye visibility may be possible during Catalina’s visit.

It is best to look for the comet at least one hour before dawn, facing east-southeast, advises Sky and Telescope magazine. Catalina will be to the left of the crescent moon and dazzling hard-to-miss Venus. Websites like skyandtelescope.com and earthsky.org have helpful graphics showing how and when to locate Catalina as it progresses through the sky in the coming weeks.

A Ball of Ice
On first discovery, Catalina was classified as an asteroid and given the memorable name “C/2013 US10.” But as it neared the sun, it developed the characteristic “fuzz” of comets, which are often described as “dirty snowballs” or “icy mudballs,” says Mark Hammergren, Ph.D., an astronomer at the Adler Planetarium and an Evanston resident.

 “Comets are substantially icy,” says Dr. Hammergren, “and have a fair amount of water ice, frozen gases like carbon dioxide (dry ice), carbon monoxide, and others. We distinguish them from asteroids when the sun’s heat starts to vaporize these frozen gases and water into the beautiful comet tail we are familiar with.”

 Comets commonly have two tails:  one composed of dust blowing off the comet, and the other of vaporizing gases that glow in reaction to the solar wind. One of Comet Catalina’s tails is estimated at more than a million miles long.

Long distance traveler
Catalina has been traveling for several million years from its birthplace in the Oort Cloud – a sphere of icy “planetesimals” that envelops the entire solar system roughly 5 trillion miles from the sun. The Oort Cloud marks the farthest boundary of our solar
system. It is so far away, says Dr. Hammer-gren, that it cannot be seen easily or at all, because the sun’s light does not reach that far. Like the Kuiper Belt – a band of icy asteroids located beyond Neptune – the Oort Cloud is a reliable source for comets.

Gravity from a passing star, planet or other interstellar object probably pulled Catalina out of the Oort Cloud and onto its journey into the solar system.

Catalina follows an open or “hyperbolic” path, which Dr. Hammergren describes as U- or V-shaped, not a closed, continuous orbit like that of Halley’s comet. As a result, this will be Catalina’s only appearance here.

 “On its way to the sun,” Dr. Hammergren says, “Catalina picked up enough extra velocity that it will never come around again.” It received a gravitational push into another direction.

Viewing Tips
The darkest location – such as the lakefront – will offer the best viewing. Binoculars, warm clothing and patience are necessities – it can take 15 minutes for eyes to adjust to the dark. Although naked-eye viewing might be possible at some point during its visit, Dr. Hammergren advises lower expectations “because comets are fickle beasts.” Comet activity – their distinctive fuzz and tails – is based on their frozen gases, which can change from time to time, he says, and so far Catalina has not been brightening as much as it was expected to. He suggests Jan. 1, when the comet will be close to the bright star Arcturus; and in mid-January, when it will be “buzzing past the handle of the Big Dipper.”

Dr. Hammergren believes that view- ing the comet with other people may be even more important than a good viewing location. “If you can meet up with some amateur astronomers from a society or amateur astronomy club,” he says, “there will be help from knowledgeable people, passionate about their hobby, who will be happy to share their views and telescopes.”

Although Catalina barely seems to move from day to day, it is blazing through space at 100,000 mph and will pass closer to Earth than Mars, while its bright dawn companion, Arcturus, is trillions of miles away. Such cosmic facts can challenge Earthly notions of speed and distance, and even an experienced astronomer like Dr. Hammergren appreciates the wonder of it.

“When you can tell a comet’s movement only from one day to the next,” he says, “it’s a reminder of how far away things are out there and how big space really is.”

Meg Evans

Meg Evans has written science stories for the Evanston RoundTable since 2015, covering topics ranging from local crayfish, coyotes and cicadas to gravitational waves, medical cannabis, invasive garden...