![]() The comet was much less impressive to southern hemisphere observers than it had been in the northern hemisphere, but southerners were able to see the comet gradually fade from view during the second half of 1997. ![]() After perihelion Īfter its perihelion passage, the comet moved into the southern celestial hemisphere. The comet was visible well before the sky got fully dark each night, and while many great comets are very close to the Sun as they pass perihelion, comet Hale–Bopp was visible all night to northern hemisphere observers. It shone brighter than any star in the sky except Sirius, and its dust tail stretched 40–45 degrees across the sky. Īs it passed perihelion on April 1, 1997, the comet developed into a spectacular sight. ![]() Hale–Bopp had its closest approach to Earth on March 22, 1997, at a distance of 1.315 AU. On March 9, a solar eclipse in China, Mongolia and eastern Siberia allowed observers there to see the comet in the daytime. Īs the comet approached the Sun, it continued to brighten, shining at 2nd magnitude in February, and showing a growing pair of tails, the blue gas tail pointing straight away from the Sun and the yellowish dust tail curving away along its orbit. The Internet played a large role in encouraging the unprecedented public interest in comet Hale–Bopp. The Internet was a growing phenomenon at the time, and numerous websites that tracked the comet's progress and provided daily images from around the world became extremely popular. It was too closely aligned with the Sun to be observable during December 1996, but when it reappeared in January 1997 it was already bright enough to be seen by anyone who looked for it, even from large cities with light-polluted skies. Hale–Bopp became visible to the naked eye in May 1996, and although its rate of brightening slowed considerably during the latter half of that year, scientists were still cautiously optimistic that it would become very bright. ![]() Star map of path with 14-day motion marked Comet Kohoutek in 1973 had been touted as a 'comet of the century' and turned out to be unspectacular. However, comet scientists were wary – comets can be extremely unpredictable, and many have large outbursts at great distance only to diminish in brightness later. Its great distance and surprising activity indicated that comet Hale–Bopp might become very bright when it reached perihelion in 1997. ( Halley's Comet was more than 100 times fainter at the same distance from the Sun.) Analysis indicated later that its comet nucleus was 60☒0 kilometres in diameter, approximately six times the size of Halley's Comet. A precovery image taken at the Anglo-Australian Telescope in 1993 was found to show the then-unnoticed comet some 13 AU from the Sun, a distance at which most comets are essentially unobservable. Most comets at this distance are extremely faint, and show no discernible activity, but Hale–Bopp already had an observable coma. Hale–Bopp's orbital position was calculated as 7.2 astronomical units (AU) from the Sun, placing it between Jupiter and Saturn and by far the greatest distance from Earth at which a comet had been discovered by amateurs. The discovery was announced in International Astronomical Union circular 6187. The following morning, it was confirmed that this was a new comet, and it was given the designation C/1995 O1. I mean, by the time that telegram got here, Alan Hale had already e-mailed us three times with updated coordinates." Marsden, who had run the bureau since 1968, laughed, "Nobody sends telegrams anymore. He alerted the Central Bureau for Astronomical Telegrams through a Western Union telegram. He realized he might have spotted something new when, like Hale, he checked his star maps to determine if any other deep-sky objects were known to be near M70, and found that there were none. He was out with friends near Stanfield, Arizona, observing star clusters and galaxies when he chanced across the comet while at the eyepiece of his friend's telescope. Once he had established that the object was moving relative to the background stars, he emailed the Central Bureau for Astronomical Telegrams, the clearing house for astronomical discoveries. Hale first established that there was no other deep-sky object near M70, and then consulted a directory of known comets, finding that none were known to be in this area of the sky. The comet had an apparent magnitude of 10.5 and lay near the globular cluster M70 in the constellation of Sagittarius. Hale had spent many hundreds of hours searching for comets without success, and was tracking known comets from his driveway in New Mexico when he chanced upon Hale–Bopp just after midnight. The comet was discovered independently on July 23, 1995, by two observers, Alan Hale and Thomas Bopp, both in the United States.
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