Before Comet Hyakutake (C/1996 B2) leapt high across the celestial stage in the spring of 1996, humankind had not seen a great comet for 20 years. Anyone who was under a dark sky will not soon forget how the comet gradually unfurled its tail — a long, ghostly banner of blue light — that ultimately traversed half the night sky. The unexpected splendor of Hyakutake's tail caused many of us to push aside the telescope and marvel at the phenomenon with the unaided eye. It seemed as if we had forgotten how beautiful a comet can be.

Yet the tail was only a part — albeit a big part — of the comet's spectacular close approach to Earth. Indeed, observers who found time to glimpse Hyakutake's bright head under high magnification were rewarded by dynamic displays of Sunward jets and a tailward spine. Then, all too soon, the comet and all it had offered faded into the twilight glow. Who really had time to fathom the dynamic action going on close to the comet's nucleus when so grand a sight was before us?

Fortunately, another bright comet, Hale-Bopp (C/1995 O1), arrived, and remained visible to the naked eye for months, not days. Amateurs with even small telescopes had an opportunity to probe this comet's nuclear regions and see some of its most secretive details.

A comet is a whimsical creature. Its behavior mimics that of a cat, being largely independent of our will and wishes. Yet Hale-Bopp was a splendid telescopic sight during the summer of 1996, some nine months before the peak of its display. By then a vast array of jets spewed dust and gas from a seemingly pulsating nucleus. Multiple parabolic hoods surrounded the inner coma, and a needlelike spine occasionally appeared in the antisolar direction. Such features are sometimes fleeting, sometimes dramatic. They go through cycles of brightness and periodically have odd appearances.

The clarity of the features in Hale-Bopp's head was outstanding by historic standards. Comet expert John Bortle notes that only a handful of bright comets in the last century have displayed such distinct, near-nuclear structure — particularly when more than 0.75 astronomical unit (110 million kilometers) from the Sun. Yet Hale-Bopp even displayed conspicuous structure when more than 4 a.u. out!