You may get a chance to see a comet this month.
In addition to good weather and a little luck, all you need to see Comet 12P/Pons-Brooks are good binoculars or a telescope and a celestial map to guide you to where this celestial wanderer happens to be. The comet bears the names of two of the most renowned comet hunters of all time.
Let's first talk about how it was discovered, then how much we know about it from a historical point of view and finally, when and where to look for it.
Related: Comets: Everything you need to know about the 'dirty snowballs' of space
The discoverers
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Jean-Louis Pons (1761-1831) was a French astronomer who later became the greatest visual comet discoverer of all time. In today's world, comets are routinely found far out in space, beyond the ability to be picked up by the human eye, but are captured using robotic cameras attached to large telescopes either here on Earth, either from satellites in space.
Pons, on the other hand, made most of his discoveries with telescopes and lenses of his own design; his "Grand Chercheur" ("Great Seeker") was an instrument with a large aperture and a short focal length, similar to telescopes that our modern amateurs would call a "comet finder". Pons is known today for his visual discovery of 37 comets (still a record) between 1801 and 1827.
One such discovery occurred on July 12, 1812. When he first saw it, Pons described it as "a shapeless object without a distinct tail," but over the next month the comet became bright enough to be faintly visible to the naked eye. eye. On August 15 of that year, it reached its peak brightness at fourth magnitude (magnitude indicates the degree of brightness of an object. The lower the magnitude, the brighter the object.) The new comet also had a split tail of about three degrees.
Orbit calculations suggested that Comet Pons was periodic and took between 65 and 75 years to orbit the Sun.
On September 2, 1883, British-born American comet observer William R. Brooks (1844-1921) found it by accident. Like Pons, Brooks was a prolific discoverer of comets. In fact, his total of 27 visual discoveries is second only to Pons. It was not until the first orbital calculations of Brooks' discovery were made that it was realized that this comet and the comet found by Pons in 1812 were one of the same. So this comet now bears the surnames of both observers.
With an orbital period of about 71 years, Comet Pons-Brooks is considered a "Halley-type comet", that is, a comet with an orbital period between 20 and 200 years, often appearing only once or twice within a person's lifetime. Other comets with a similar orbital period are 13P/Olbers, 23P/Brosen-Metcalf and the best known of them all, 1P/Halley. Because it was the twelfth comet for which a definitive orbital period was calculated, it is now cataloged as 12P/Pons-Brooks.
Performances from the past
That 1883-1884 appearance of 12P/Pons-Brooks was quite auspicious because it made its closest approach to Earth of 94.3 million km on January 10, 1884, just 16 days before its closest pass to the Sun (perihelion). ) at a distance of 72.5 million miles (116.7 million km). During this time frame the comet reached third magnitude and showed a tail about 20 degrees long in binoculars.
It also appears that when this comet arrives at perihelion in late fall or early winter, it shows up at its best. In 2020, German astronomer Maik Meyer showed that the naked-eye appearance of a comet mentioned by the Chinese in November 1385, and another observed by an Italian astronomer in January 1457, were probably relatively bright appearances of 12P/Pons-Brooks. And there is some evidence that an old record of a bright comet from 245 AD could also have been 12P.
Also of particular interest in the period 1883-1884 was that this comet was apparently prone to sudden bursts or flares in brightness on a few occasions, leading to its being labeled a famously erratic comet.
On its way to its next return to the Sun in May 1954, 12P/Pons-Brooks experienced four more unexpected eruptions. But at its closest to Earth that year, the comet was more than 2.5 times further away than in 1884 and so was not as bright or impressive, peaking at magnitude +6.4 (near the threshold of visibility to the naked eye) and produced a tail that was only half a degree long.
Flare supply
This year, 12P/Pons-Brooks will arrive at perihelion on April 21, but it is already up to its old tricks regarding sudden flares in brightness. Last July 20, an unexpected brightness burst briefly made it about 100 times brighter and the shell of expanding gas around the core (called the coma) expanded, resembling a horseshoe to some.
Others, however, suggested a horseshoe crab, the Millennium Falcon from Star Wars, the cartoon character Yosemite Sam, or even - as many news media put it - the horns of a devil, a.k.a. "The Devil's Comet." Other eruptions occurred on October 5, November 1 and 14, December 14, and most recently on January 18.
And more eruptions look possible as we move through this month.
The exact cause of these eruptions is unknown, although Richard Miles of the British Astronomical Association believes 12P is one of ten to twenty known comets with active ice volcanoes. The "magma" is a cold mixture of liquid hydrocarbons and dissolved gases, all trapped beneath a surface that has the consistency of wax. These pent-up volatiles can explode when sunlight opens a crack.
For this reason, some have called 12P a 'cryovolcanic comet'.
Tracking the comet
From now until the end of March, 12P/Pons-Brooks will be visible in the early evening sky, in the constellation Andromeda the Princess, at the upper left of the Great Square of Pegasus, about 20 degrees above west. -northwest horizon at the end of evening twilight.
With the help of a good sky map and a dark sky it should be easily accessible with binoculars. Its apparent motion from night to night will now speed up as it gets closer to the sun. By the middle of the month it will have changed to Pisces, the Pisces; now perhaps a 6th magnitude object, it should be a nice sight for binoculars.
And by the end of March it may brighten to a magnitude of 5, becoming visible to the naked eye against the backdrop of the constellation Aries. A short tail may have also formed by now.
The comet will then fade into sunset glow in April and arrive at perihelion on April 21 at a distance of 72.6 million miles (116.8 million km). 12P/Pons-Brooks will pass 22 degrees northeast of the Sun in mid-April, but will then fade very quickly and become largely an object to Southern Hemisphere observers. It will likely drop to magnitude 6 or 7 by the end of May and to magnitude 8 or 9 by the end of June.
Future eruptions and the solar eclipse
It is claimed that if 12P/Pons-Brooks were to experience another flare-up in the coming weeks, it could become a very bright and even spectacular object. Unfortunately, that doesn't seem likely. Space.com asked noted comet expert John Bortle for an assessment of how the comet might "perform" in the coming days.
He believes that although 12P/Pons-Brooks brightened dramatically last summer when the comet was far from the Sun and just beginning to become active, any flare-ups in the near future will not make the comet appear much brighter. because the overall brightness of the comet has increased significantly as it has now moved much closer to the Sun.
"As a result," Bortle notes, "the brightness of the outburst cannot so easily overwhelm the overall brightness of the comet's coma."
Thus, any additional outbursts or eruptions will likely result in only a small increase in the comet's brightness.
There is also talk that 12P could be visible during the total solar eclipse on April 8. "But," Bortle adds, "I would think that's much more of a fantasy than anything." The comet is not expected to become much brighter than magnitude +4.5 around the eclipse; far too faint - even with a little help from a flare - to see.
The next time?
After 12P/Pons-Brooks returns to space, it will take another 71 years for it to complete another full circuit around the Sun. For most of us, this year's performance will be the only time we'll see it.
But the very young people who are there now may get a second chance in the summer of 2095. Japanese orbital expert Hiroshi Kinoshita of the National Astronomical Observatory of Japan (NAOJ) has calculated that 12P will arrive at perihelion on August 10 that year. year.
If you want to see Comet 12P/Pons-Brooks or another comet for yourself in the night sky, our guides to the best telescopes and best binoculars are a good place to start.
And if you want to take photos of Comet 12P/Pons-Brooks or the night sky in general, check out our guide to viewing and photographing comets, as well as our best cameras for astrophotography and the best lenses for astrophotography.
Joe Rao is an instructor and guest lecturer in New York Hayden Planetarium. He prescribes on astronomy Natural history magazinethe Farmer's almanac and other publications.
