If you remember the spring of 1997, you probably remember Hale-Bopp Comet. Bigger and brighter than most previous comets, Hale-Bopp made its closest approach to earth on March 22, 1997.
Hale-Bopp, discovered by amateur astronomers Alan Hale and Thomas Bopp simultaneously in 1996, was 1,000 times brighter than its famous cousin, Halley's Comet. Visible for more than 18 months in the Northern Hemisphere, it was one of the largest known comets, with a tail more than 25 miles in diameter. Since it appeared just as the Internet was gaining popularity, news of sightings spread quickly -- by the end of April, 1997, more than 70 percent of Americans had seen the comet.
Unlike Halley's Comet, which is a short-period comet that appears once every 75 or 76 years, Hale-Bopp only appears once every several thousand years, making it a new discovery in the 90s. It is suspected to have come through the solar system in 2215 B.C., when it had a near-collision with Jupiter. Given its long orbit, it was observed intensively during its 1997 loop, and was determined to have a sodium in its tail, which had not been observed in comets previously. Although the discoveries were plentiful, the comet is not expected again until 4385.
As a tragic coda, 39 members of a San Francisco-based doomsday cult committed mass suicide on March 26, 1997, believing that by doing so, they would reach an alien spacecraft following Hale-Bopp.