Among all the comets that blaze through Earth’s small sector of space, relatively few are spectacular enough to earn the honorific great. There are no objective standards for admission to the club. Naked-eye visibility alone won’t do it. For a comet to be considered great, it must be striking to the public at large; it must be immediately obvious to anyone glancing up into the sky. Suffice it to say that when astronomers talk about a great comet, they’re talking about a cosmic visitation that’s positively awe-inspiring.
Great comets arrive every 15 years, on average, but we haven’t seen one since Comet West in 1976 (shown in photo above); Halley’s 1986 visit was, to some sky watchers, a fizzle. With Hyakutake’s sudden arrival this past spring, however, it seemed the great comet drought had ended. Indeed, even before Hyakutake burst onto the scene, astronomers were gearing up for another great comet contender, the leisurely incoming Hale- Bopp. With comets, it’s either feast or famine, and now it’s finally our turn at the banquet table.
Such a repast is not unprecedented. In 1910 people gaped at the Great January Comet, which could be seen in broad daylight; a few months later they enjoyed a fabulous view of Halley. Unfortunately, it’s more common to have a decade or more go by with nothing better than faint telescopic teasers.
As we observe the exciting, brightening Hale-Bopp this month, we might first take time to close the book on outgoing Hyakutake, since astronomers have been hotly debating whether it deserves the Great Comet crown. Some experts insist that a great comet must be bright enough to appear over light-polluted skies. Hyakutake’s tail hovered within a single magnitude of naked-eye visibility and so was swamped by the milky mess above urban and suburban regions. To most of us, then, the comet had no tail and looked like a small oval blur: nothing special, and surely not great.
Wrong, says renowned comet expert John Bortle. To Bortle, Hyakutake’s huge head and 45-degree tail, spanning half the distance from horizon to zenith, made it not only a great comet but the best comet in several centuries--regardless of how many of us saw its splendor. My vote: From any rural setting, Hyakutake was nothing less than awesome. A great comet, for sure.
Hale-Bopp should be greater. The comet became visible to the naked eye early this summer and continues to brighten as it falls toward us. Late next March, Hale-Bopp will pass about 100 million miles from both Earth and the sun--not very close--but should then shine brilliantly. Its dazzling white tail of dust (wider and shorter than Hyakutake’s long, thin blue plume of plasma) will almost certainly materialize for city dwellers. Hale-Bopp is a Goliath--a monster comet.
But you don’t have to wait until spring to catch a glimpse. The first half of November offers an ideal dress rehearsal, since the moon will be absent until the thirteenth. Hale-Bopp should shine between magnitude 4 and 5 this month--a medium-faint object easily seen from rural skies. At 6 p.m. (or as soon as full darkness falls), look for Jupiter in the southwest--the brightest star in the heavens. Measure off one outstretched hand (with fingers spread) at arm’s length to the upper right of Jupiter and you’ll find Hale-Bopp. Sweep the region with binoculars and it should really pop, or Bopp, into view.
Next month the comet is lost in the sun’s glare, but it returns in January, in the eastern sky before dawn. Then comes the March and April climax. And in all probability, sky watchers will consider it great.
