Comet Hale-Bopp is Discovered

Comet Hale-Bopp was arguably the most widely observed comet of the twentieth century, and one of the brightest seen for many decades.

It was visible to the naked eye for a record 18 months, twice as long as the previous record holder, the Great Comet of 1811.

Hale-Bopp was discovered on July 23, 1995 at a great distance from the Sun, raising expectations that the comet would brighten considerably by the time it passed close to Earth. Although predicting the brightness of comets with any degree of accuracy is very difficult, Hale-Bopp met or exceeded most predictions when it passed perihelion on April 1, 1997. The comet was dubbed the Great Comet of 1997.

The passage of Hale-Bopp was notable also for inciting a comet-related panic. Rumours that an alien spacecraft was following the comet gained remarkable currency, and inspired a mass suicide among followers of the Heaven's Gate cult.

Comet Hale-Bopp was discovered on July 23, 1995 by Alan Hale, the founder and Director of the Southwest Institute for Space Research, and independently by Thomas Bopp, an amateur astronomer from Glendale, Arizona.

At the time of its discovery the comet was a dim and unimpressive object not dramatically different in appearance from the dozen or more comets that are discovered every year, however orbital calculations soon revealed that Hale-Bopp was at the enormous distance of 7.15 Astronomical Units (665 million miles, or 1.1 billion km) from the sun. Furthermore, these calculations also showed that the comet was over a year and a half away from its closest approaches to the sun and earth, at which time it had the potential of providing a brilliant celestial display.

On July 23, 1995, an unusually bright comet outside of Jupiter's orbit (7.15 AU!) was discovered independently by Alan Hale, New Mexico and Thomas Bopp, Arizona. The new comet, designated C/1995 O1, is the farthest comet ever discovered by amateurs and appeared 1000 times brighter than Comet Halley did at the same distance. Normally, comets are inert when they are beyond the orbit of Jupiter, so it has been speculated that Comet Hale-Bopp is either a rather large comet or experienced a bright outburst (or both). The comet is the brightest comet since Comet West in 1976. From Hubble Space Telescope images, the comet's diameter has been determined to be about 40 km. The Pic du Midi Observatory has ascertained from their observations that the comet's rotation rate is 11.4 hours.