Photo courtesy of University of Arizona, Science Skylab

“Comets are like cats. They do precisely what they want” –David Levy, Astronomer

Sometimes, being an astronomer is a lot like being a weather forecaster. I would love to predict astronomical events with 100 percent certainty. However, experience has taught me to hedge my predictions with a healthy dose of skepticism.

Halley’s Comet Was Hazardous to Their Health.

The Aztec Emperor Montezuma’s astrologers were not so lucky. They failed to predict the appearance of Halley’s Comet. So he had them killed. I’m relieved times have changed in that I’m wrong, frequently.

In the words of the late astronomer, Carl Sagan, comets have been viewed through history as “harbingers of disaster.” Some historians believe that the apparition of Halley’s Comet in 1066 inspired the Norman invasion of England. Comets have been said to be predictors of the death of rulers and fall of kingdoms.

Not All Superstition is Ancient.

We can laugh at ancient superstitions, but we need only look back as far as 1997, when San Diego’s Heaven’s Gate cult interpreted a Hubble Space Telescope photograph of Comet Hale-Bopp as having a spaceship following the comet. They believed that when they committed mass suicide their souls would be “beamed up” to the ship. Who am I to say they were wrong?

What are Comets?

Comets are relics of our solar system’s formation. They formed in the outer reaches of our solar system more than 4.5 billion years ago. They are mostly made of water ice, traces of methane and ammonia ice, and a substantial amount of rock and dust. In 1950, astronomer Fred Whipple coined the term “dirty snowball” to describe the nucleus of a comet.

Most of a comet’s life is spent orbiting the sun outside the orbit of Neptune in the Kuiper Belt, or in a distant spherical halo surrounding our solar system called the Oort cloud. When something disturbs the orbits of these icy mountains, they begin their path toward the sun. It’s not until they cross the orbit of Jupiter that the sun’s radiant energy becomes great enough for them to begin to vaporize and form what’s called a “coma” surrounding the nucleus, and a tail marking its path. When the Earth passes through the debris left by comets, we have meteor showers named after the constellation from which the meteors appear to radiate.

Famous Comets.

It’s been a while since we had a “great comet” in our night sky. Halley’s Comet was a bit of a disappointment in 1986. But 10 years later, Comet Hyakutake brightened the night sky and Comet Hale-Bopp put on a great show a year after that.

Comet ISON.

Comets are named after their discoverers. Comet ISON was discovered by Vitali Nevki and Artyom Novichonok in Russia at an observatory that is a member of an organization called the International Scientific Optical Network (ISON). So every comet discovered by this network is called ISON.

What makes ISON so intriguing is that it will pass very close to the sun. On Nov. 28 (Thanksgiving), ISON will pass a little more than a million kilometers (730,000 miles) from the sun. This will heat the surface of ISON to more than 2000°C (3600°F). Astronomers are truly unsure if the comet will actually stay intact after this close pass, but most are in agreement that it will cause the comet to brighten significantly.

When and Where to Look for Comet ISON.

The best time to see this comet is about an hour before sunrise in the east-southeastern sky. Binoculars or a telephoto lens are best in that the tail of the comet will extend beyond the field of view of most telescopes.

As we move into December, the comet will trail off into the northern sky. It will be possible to see it in the evening sky, although it will dim rapidly. I’m hoping to spot it at our Sunlight Peak Open House, Friday Dec. 6. If we don’t spot the comet, I certainly hope you treat me with a little more compassion than Montezuma showed his astrologers.

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