A comet long considered lost has been found again!
Comet Pons-Gambart was discovered on June 21, 1827 by Jean Louis Pons, observing from Florence, Italy and Adolphe Gambart in Marseilles, France. It brightened to the naked-eye limit (between 5th and 6th magnitude) and then quickly faded. Pons last observed the comet on July 21, 1827 calling it “very faint”.
With only a month of observations, no one bothered to determine an orbit for the comet until a year later. Based on those calculations, it appeared that Pons-Gambart was like many comets, one-hit wonders destined to never return.
Fast forward to 1917 when a second look at the data by astronomer Dr. S. Ogura led him to calculate an elliptical orbit. A comet in an elliptical orbit regularly cycles around the sun making repeat visits. The length of time between visits is called its period. Ogura predicted a period of just under 64 years for Pons-Gambart with an uncertainty of +/- 10 years. Further investigation of its orbit in 1978 gave a period of 58 years plus or minus 10.
We knew it was a repeat or periodic comet, but with no observations since 1827, it appeared hopelessly lost. Hence its official name as D/1827 Pons-Gambart, the “D” meaning lost or deceased.
Then came a happy turn of events. In November, space scientist and amateur astronomer Rob Matson of Newport Coast, Calif. spotted and tracked a comet in pictures taken by the SWAN camera aboard the Solar Heliospheric Observatory (SOHO). Matson put out a call via e-mail for confirmation photos from the ground. Battling trees and moonlight, Australian amateur Terry Lovejoy photographed and confirmed the comet just two days later on Nov. 29.
Preliminary calculation of its orbit shows an excellent fit to Pons-Gambart’s. Despite being missed on two previous flybys, this welcome stranger has returned home.
Reincarnated now as comet C/2012 V4, it reaches perihelion, the point in its orbit closest to the sun, on Dec. 18 at a distance of about 75 million miles. Astronomer Rob McNaught described its appearance as a “spring onion” with bright fuzzy core and short spike of a tail to the northeast.
Based on the present return date, we can figure Pons-Gambart’s period at about 62 years. After discovery in 1827, its appearances in 1889 and 1951 were missed, but thanks to space-based cameras and Matson’s keen eye, this time the comet didn’t get away.
Next question – can you see it? No problem if you live in the far southern U.S. and points further south. Skywatchers in South America and Australia have the best view. It’s currently about magnitude 9.5 and visible in 4.5-inch and larger telescopes in the constellation Sagittarius. From mid-northern latitudes, it might be visible with a bigger scope (8 inches and up) very, very low in the southwestern sky at dusk in the coming week.
You can use the map above to help you find it – just right-click, save and print out a copy. One big help in locating the comet is its proximity to the planet Mars (not for real, just line of sight). On the 7th, the two will be in conjunction less than 1 degree apart!
Over the next few weeks, C/2012 V4 will stay fairly close to the sun; not until mid-January will northerners have a better shot at seeing it, when the comet tracks through the constellations Scutum and Aquila in the pre-dawn sky. Pons-Gambart shines brightest now through mid-December and then slowly fades. I hope at least some of you will be able to put out the welcome mat for this lost soul. There’s a thrill in finding a comet that no one’s seen hide nor hair of in 185 years.