Comet’s arrival may be a flop

It could be the most spectacular comet to approach our planet in generations, astronomers are saying. It could be brighter than the full moon, they are saying. The comet’s fiery tail by next winter could be visible even in daytime, they are saying.

Prepare for astronomical disappointment, I am saying.

These great comets come around every few years, always with great fanfare. Then comes the great fizzle.

The astronomical spectacle of the ages this time is comet Ison, hurtling into play even now from the solar system’s extreme outer limits. Ison by late next fall will come within 63 million kilometres of the Earth. In astronomical terms, that’s our front yard. The prospects for a celestial light show have not been as good since the Great Comet of 2007.

You probably don’t remember the Great Comet of 2007. The brightest comet in 40 years, it reportedly was visible to the naked eye in January of that year, but good luck finding anyone who actually saw the thing except through a powerful telescope. That this is billed as great reveals how low is the standard of greatness here. A Bic lighter at 200 yards would qualify.

Preceding the Great Comet of 2007 were several not-so-great comets. These were so dim we could only take astronomers’ word for it that they were out there at all, like black holes and dark matter, astronomy’s invisible friend.

The last comet to generate any excitement was Kohoutek, named for the unfortunate Czech astronomer who discovered it while scanning for asteroids in the spring of 1973. Prepare for the comet of the century, we soon thereafter were told. Comet Kohoutek was going to light up the sky like a magnesium parachute flare. When it finally arrived, however, Kohoutek was indistinguishable from a speck of dust on the lens of your eyeglasses. The name Kohoutek thereafter became synonymous with dud.

Too bad for Lubos Kohoutek. He was a distinguished astronomer who also discovered dozens of asteroids and published more than 160 scientific papers, but it’s the dud that everyone remembers. He later would say it was journalists, not astronomers, who oversold the comet, as if journalists ever would have heard of it had astronomers not been all jacked up.

Kohoutek was just a bitesize sample of astronomical disappointment to come.

That would be Halley’s comet, until quite recently the most celebrated and reliable of comets.

Halley’s zooms around the sun and past the Earth like clockwork every 76 years. For more than 2,000 years, astronomers have observed and recorded its regular appearances. The breakthrough came in 1705 when English Astronomer Edmond Halley became the first to predict when next the comet would return.

Halley’s comet last appeared in 1982. I was among those who could hardly wait. I had seen pictures of the ancient Bayeux Tapestry illustrating the comet’s appearance in 1066. It is depicted as a flaming wagon towed across the sky by a ball of fire. How I yearned to see this ancient wonder. As a schoolboy, I calculated my age when the awesome comet was to reappear. Thirty-two. I hoped I would live so long.

Reports of Halley’s last appearance in 1910 only fuelled my enthusiasm. It then was bright enough to scare people. So close was the comet that the Earth actually passed through its tail, provoking widespread fears that atmospheric poisoning would extinguish all life on Earth. Reputable astronomers were not among the alarmists. The tail was too diffuse to matter, they correctly predicted.

Astronomers did nothing to diminish expectations for another terrific Halley’s flyby in 1982. They were as surprised as anyone else when its appearance, if you can call it that, was utterly unimpressive. Only after the fact did they conclude that, due to the comet and the Earth lining up on opposite sides of the sun, this was the worst viewing in more than 2,000 years. Even through binoculars, it appeared smaller than the apostrophe in Halley’s.

Now comes Ison, named for the International Scientific Optical Network observatory in Russia where astronomers discovered the incoming comet. This time, it is not journalists predicting something spectacular. This time, it is NASA, among others, saying comet Ison might shine brighter than the full moon. The space agency further advises we might also be in for a spectacular meteor shower as the Earth passes through Ison’s tail.

“Might” is the operative word here. It also means “might not.” That’s more what we expect from dice than from science.