Waiting For the Big One
Not the Big One. Comet PanSTARRS in the evening sky on March 22nd.
One aspect of being an avid sky watcher is that the passage of time isn’t marked just with pages in a calendar, but also by gaps — the spaces between “once-in-a-lifetime” events. It's been over 15 years since Comet Hale-Bopp visited the inner solar system and the gap widens with each passing year spent watching amd waiting for the arrival of the next great comet. Could the wait finally be ending?
Comet Hyakutake, March 24, 1996. The Big Dipper (upper left) gives some sense of scale — the comet’s tail spanned more than 50°!
As fine an object as Comet PanSTARRS has turned out to be, it's no Hale-Bopp. Far from being a once-in-a-lifetime comet, it's more along the lines of a once-every-couple-of-years object. But the drought might end this autumn with the arriveal of Comet ISON. It's too soon to tell what will happen with much certaintly, but the potential for something that is truly once-in-lifetime is there. ISON may even be bright enough to be seen in full daylight. Now that would be something!
Many casual sky watchers thought Hale-Bopp a once-in-a-lifetime event, but even at the time it wasn't. Just a year earlier, another bright comet unexpectedly appeared: Comet Hyakutake. Unlike Hale-Bopp, which we saw approaching years in advance, Hyakutake came and went like a late-afternoon thunderstorm — almost before we knew it, it had swung by the Earth and was retreating back into the cold depths of space from whence it came. Depending on your sky conditions, it was even more spectacular than Hale-Bopp. On the night of closest approach, Hyakutake shone like a beautiful blue-green beacon from the handle of the Big Dipper, with a delicate searchlight-beam of a tail that stretched across the sky.
Those two springtime comets hold special significance for observers of my generation. Up until they arrived, many of us felt positively snake bit when it came to comets. I was too young and unaware to see the great sungrazer of 1965, Comet Ikeya–Seki. However, I was old enough to enjoy the bitter disappointment of 1973’s no-show "comet of the century," Comet Kohoutek. Comet West? Like a lot of other astronomers in 1976, I only heard about that magnificent visitor long after it had come and gone. And don’t get me started on how defeated I felt when Halley's Comet – the one “sure bet” of my astronomical life – failed to live up to expectations. But in spite of all those dashed hopes and missed opportunities, I have to admit that getting to see not one, but two great comets in the span of just a single year, more than made up for it.
And now, 15+ years later, we may witness a comet so spectacular that both Hale-Bopp and Hyakute will seem like feeble also-rans by comparison. Here's hoping Comet ISON is more like those two than Kohoutek or Halley.
Comet Hale-Bopp photographed on the evening of April 3rd, 1997.