Within days after a new comet is first discovered, astronomers
can tell you exactly what its path through the solar system will
look like. They can calculate when it will make its closest
approach to the Sun, how near it will be to Earth at any given
moment and even when — or whether — it’s likely to make a return
visit. What they can’t say for sure is how brilliant a show it
will put on for us. Back in the 1970’s, Comet Kohoutek was
billed as the “Comet of the Century,” but it turned out to be so
disappointing that it ended up as a laugh line for Johnny Carson
on the Tonight Show. Even a well-known comet like Halley’s,
whose 1986 appearance was ballyhooed years in advance, can turn
out to be a dud. With that caveat noted, however, there’s a
reasonable chance that Earth is in for a celestial display just
about a year from now. Comet ISON, discovered by two amateurs —
one from Belarus, one from Russia — in September, shows early
signs of being truly spectacular. At its brightest, in fact,
ISON could put out as