![]() ![]() ( 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. They should also know more soon about the comet's temperature, spin and shape.The comet was discovered independently on July 23, 1995, by two observers, Alan Hale and Thomas Bopp, both in the United States. Large telescopes like the Atacama Array will allow scientists to learn more about the chemical composition of the comet as it passes, Lellouch and his colleagues wrote. The comet will not be visible to the naked eye, as Hale-Bopp was at its closest approach, but scientists expect to learn a lot about Oort Cloud objects from the visitor. As the comet gets closer to the sun, its tail of dust and gas will expand, and its main body will melt and shrink. It's exciting to get a measurement while the comet is still so distant, the researchers added, because Bernardinelli-Bernstein will likely shrink significantly by the time it gets closer to Earth. This is the longest distance at which this type of measurement has been done before, the researchers wrote in their new paper. From these reflected light wavelengths, the team could infer the comet's size. (An AU is the distance between the Earth and the sun and translates to about 93 million miles, or 150 million kilometers.) Researchers studied the microwave radiation (opens in new tab) coming off the comet's bulk. ![]() The new research was led by Emmanuel Lellouch, an astronomer at the Observatoire de Paris, and used data from the Atacama Large Millimeter Array in South America, taken in August 2021 when the comet was 19.6 AUs away. Cosmic record-holders: The 12 biggest objects in the known universe The 10 strangest space structures discovered in 2021 The 12 strangest objects in the universe ![]()
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