Past and Present visits of the Pons-Winnecke Comet
CLOSER TO THE EARTH than any comet except one is known to have come before, the Pons-Winnecke comet was only 3,500,000 miles away from us on June 27, about fourteen and a half times as far as the moon, and far closer than any other astronomical body ordinarily comes.
But despite this neighborly visit, says Science Service's Daily Science News Bulletin (Washington), no empires fell because of its proximity, and no kings passed away. In fact, no signs at all appeared in the sky, for it is quite doubtful if the comet was visible to the unaided eye, and even if visible, it was a mere faint patch of light, quite different from the usual conception of a comet, for in the ten previous visits on which it has been observed by astronomers, it has never shown any trace of a tail. We read further:
"The mere fact that it is coming so close makes it interesting to the astronomical profession, and for the next month or two it will be the cynosure of telescopes large and small. Only once, so far as astronomers know, has a comet come anywhere near as close as Pons-Winnecke. That was in 1770, when Lexell's comet approached to a mere stone's throw of 1,400,000 miles from the earth. Probably within a few years after that, many people thought that it had been a warning of the American Revolution, for until comparatively recent times superstition about comets has been rampant. They were supposed to be the heralds of wars and conquests.
"Halley's comet, for instance, which visited the neighborhood of the earth last in 1910, was supposed to foretell the Norman Conquest when it came in 1066. On the famous Bayeux Tapestry the comet is depicted as King Harold views it in alarm, possibly with some fear of the future work of William the Conqueror, which cost him his throne. And then, as Halley's comet appeared again in 1910, these early historians would probably have supposed that it foretold the Great War.
"Halley's comet is one of respectable size, even tho it is by no means the biggest. Pons-Winnecke, however, is rather a second-rate comet, as far as size is concerned. It is a periodic comet, and returns once in a little over six years to the neighborhood of the earth. A French astronomer at Marseilles, named Pons, discovered it in 1819, but it was not found on the next few visits. In 1858, however, a German astronomer, at the University of Bonn, Winnecke by name, discovered a comet. After a few observations of his comet had been made, it was found that it was the long-lost Pons comet, and in honor of his having rediscovered it, the German's name was attached, making it the Pons-Winnecke comet.
"In the following years, constant track has been kept of it, tho some of its returns have not been observed. It was seen in 1869, 1875, 1886, 1892, 1898, 1909, 1915, and 1921. It came back also in 1880 and 1904, but in those years it was not in a good position, and so it was missed. This year an American astronomer had the honor of being the first to find it, for Prof. George Van Biesbroeck, of the Yerkes Observatory of the University of Chicago, sighted it on March 3, with the observatory's reflecting telescope, in which a dish-shaped mirror two feet in diameter serves the same function as the lens of the refracting telescope.
"The comet's path is an ellipse, one end of which is near the sun, the other out beyond the orbit of Jupiter, which is itself 483 million miles from the sun. When closest to the sun, at what the astronomer calls perihelion, it is just a little farther away from that luminary than we are. The earth is about 93 million miles from the sun, and the comet is about three and a half million miles farther. This year it happens that the comet comes to perihelion at about the same time that the earth is in the part of its orbit nearest the comet orbit. If it were coming six months from now, then the earth would be on the opposite side of its orbit, and the comet would be about 190 million miles away.
"But the earth, as a matter of fact, has very little effect on a comet. Out in the part of its orbit farthest from the sun, even a large comet, like Halley's, is very faint and inconspicuous, entirely invisible to the best of our telescopes. And then, as it approaches the sun, it is excited to activity and may get very bright if it comes very close to the sun, tho all this is at its own expense. The tail, and all the stuff that is thrown off from a comet, leaves it, never to return, so that comets are all gradually wasting away. Without doubt, the day will finally come when Halley's comet will be no more.
"Pons-Winnecke, however, will not come any nearer to the sun than it has in past years, about 96 million miles from it, and so it will not get particularly excited about the proximity of such a relatively unimportant planet as the earth. Even when it gets near Jupiter, largest member of the solar system, it is not excited to activity, tho that big planet can, by his gravitational attraction, pull the comet out of its old orbit, and into a new one if it gets too close.
"Just what a comet consists of is not definitely known, but whatever it is, the stuff is very sparsely scattered. It is really no denser than the vacuum obtainable with the best of our air pumps. Stars can be seen in undiminished brightness through even a comet's head, and even when a comet has passed between us and the sun, it has been entirely invisible. But the spectroscope often shows carbon monoxid, the same poisonous gas that is given off by automobile exhausts, in a comet's tail. Other gases, many of them poisonous, have been found in comets as well, but since they are so exceedingly rarefied, the people of the earth would probably not be poisoned even if we have a head-on collision with a comet. Perhaps the only effect would be a shower of meteors, or shooting stars, if the collision occurred at night!"
Source: The Literary Digest for July 16, 1927
NOTE: The 1927 appearance was the best since Pons-Winnecke's discovery. It passed only 0.0404 AU from Earth on June 26, 1927 and attained a maximum brightness of magnitude 3.5.