|The Discovery of a Great Comet|
Jim Stevens leaned over the chart table, the surrounding darkness broken only by the dull red glow of his flashlight. Stevens and several friends had gathered for a night of deep-sky observing at Vekol Ranch about 90 miles south of Phoenix, Arizona. The group had begun the night by observing the Veil Nebula, a supernova remnant whose feathery detail bellies a violent explosion which abruptly ended a star's life some 30,000 years ago. The group had since moved into the southern sky to hunt globular star clusters in Sagittarius. The waning crescent Moon was still several hours from rising when Stevens began scanning Sky Atlas 2000, chart 22, searching for the next target.
A few feet away, Thomas Bopp peered into the eyepiece of Stevens' home-built 17.5-inch Dobsonian telescope. Bopp was studying M70, an 8th magnitude globular cluster located between Epsilon and Zeta Sagittarii. He watched as the cluster quietly passed through the field of view and, after a few moments, noticed a faint patch of light emerging from the northeast. Bopp centered the new object and called to his observing companion, "Jim, what's this near M70?" Jim Stevens walked over, stared into the eyepiece and saw something that shouldn't have been there. While Bopp continued observing, Stevens pulled out volume two of Uranometria, turned to page 378 and confirmed his suspicion. Nothing was plotted where Tom Bopp's object appeared. It was 11:00pm MST July 22, 1995.
Three hundred miles to the southeast in Cloudcroft, New Mexico, Alan Hale was looking at the same mysterious patch of light with his 16-inch equatorial Newtonian. Hale, an experienced comet hunter with over 200 observations to his credit, had just begun a deep-sky tour through Sagittarius to help fill the time until comet d'Arrest would be high enough for observation. Hale's first stop was M70. He immediately noticed a soft 10th magnitude glow about 15 arc minutes to the northeast of the bright globular star cluster. This object had not been there two weeks earlier during Hale's last observation of M70.
Patiently, Hale went through his new object identification routine. First, he confirmed that he was indeed observing M70 and not one of the many other globular clusters in Sagittarius. Then, Hale drew a sketch of the field and made a brightness estimate of the object. Hale then went into his home office to check several deep-sky catalogues but found no 10th magnitude object plotted near M70. That eliminated star clusters, nebulae and galaxies as possibilities. To determine if he had run across a known comet, Hale fired up his computer and logged onto the International Astronomical Union (IAU) Minor Planet Center's computer in Cambridge, Massachusetts. He ran the comet-identification program but, again, nothing. Finally, Alan Hale returned to his telescope to look for the one defining clue that this was a comet. Suspicion confirmed, Hale returned to his office. At approximately 12:50am MDT on July 23, Alan Hale sent an email-mail to Brian Marsden and Daniel Green at the IAU Central Bureau for Astronomical Telegrams, informing them of a possible new comet.
"Tom, you might have something," said Jim Stevens. None of Steven's charts indicated an object where Bopp's discovery appeared. That left two possibilities, either this was an unplotted deep-sky object or a comet. Star clusters, emission nebulae and galaxies do not change position relative to the background stars. Comets do. The group decided to watch Bopp's object to see if it changed position. Bopp, Stevens and others watched as the object's position did change ever so slightly over the next 75 minutes. This was the same test that Alan Hale had completed just minutes earlier. At 12:25am MST, Tom Bopp began the 90-mile drive home to report his find. It was nearly 3:00am before Bopp's discovery announcement arrived by telegram at the Central Bureau.
Though exhausted from being up all night, Tom Bopp could not sleep. Anxiously, he waited for a phone call that would either confirm or refute his discovery. He didn't have long to wait. Just after 8:00am, Bopp received a call from Brian Marsden, "Congratulations Tom, I believe you've discovered a new comet."
Thus, the most-observed comet in history was discovered on the same night by two amateur astronomers. Comet C/1995 O1 (Hale-Bopp) has been under nearly constant observation since July 1995. By April 1997, it had brightened enough to be easily visible to the naked eye. Millions around the world were treated to Hale-Bopp's brilliant display that spring. Today, professional astronomers continue to study and observe the comet. No other comet in history has remained observable as long as Hale-Bopp.
Click on the below links to see my sketches and observations of the Great Comet of the 20th Century.
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