By Ron Cowen
In less than 24 hours, a small, faint comet became 400,000 times brighter late last month, blossoming into a fuzzy, starlike apparition visible to the naked eye. Now, 3 weeks after its spectacular flare-up, Comet 17P/Holmes remains visible to the naked eye in the constellation Perseus, which stands nearly overhead from the United States soon after midnight.
Many comets brighten as they near the sun. Heat vaporizes volatile ices on a comet’s surface, throwing out fine, highly reflective dust particles in the process. But Holmes, which has a 6.88-year orbit, never gets any closer to the sun than twice Earth’s distance. Even more puzzling, the brightening took place about 5 months after the comet’s closest approach.