Halley’s Comet after 75 years rushes earthward again
by Mary Procter
Whence art thou, say, thou pale winged messenger? And whither goest? What thy history? And what thy future? Tell a waiting world Ere visiting again yon silent deeps.
After an absence of 75 years, Halley’s comet (so named after the astronomer who determined its orbit) is on a return trip. The magnified eyes provided by scientists in the giant lenses of the telescopes at the Lick and Yerkes observatories will be enabled to get a glimpse of the returning wanderer from space in the fall of the present year. As the comet approaches nearer and nearer to our planet, the smaller telescopes will have their chance.
The benefit of the camera
The surprising fact, however, is noted by Professor E E Barnard of the Yerkes observatory, that the comet will be found by the camera before it can be picked up by the greatest telescopes.
In reply to questions regarding the expected return of Halley’s comet, I have received the following interesting reply from Professor Barnard. He is an eminent authority on the subject and is well known for his remarkable work in celestial photography, especially in the photographs he has taken of comets. In this way we have learned much of the marvelous changes these celestial visitants from the sky undergo while journeying through space.
By means of photography, a new chapter will be added to our knowledge of the peculiar characteristics of Halley’s comet, and doubtless many fine photographs of the wanderer will be obtained before it recedes on its return trip through space.
“I think you can say with absolute certainty,” says Professor Barnard, “that Halley’s comet will be visible in the 40 inch telescope in the winter of 1908. It ought to be a bright object then in a good telescope, and should be visible in any telescope of five or six inches aperture, because, according to Holetchek (Astr. Nach. for 1908, June 13) it will on October 2, 1909, be of the fourteenth magnitude. It will, of course, get brighter after that date.
“On October 2, 1908, it will be unusually faint, because its computed magnitude will be 18.2m. According to Dr Holetchek, the brightness of the comet at its best will be 3.7m. This would make it not very different from the brightness of Daniel’s comet of that year. But you must bear in mind that a comet is an uncertain quantity, so far as a prediction of its brightness is concerned, and it may come up to some of its glory of the middle ages, though this is not probable, for the comet at each return must lose a great deal of its tail producing material, and hence at each successive return, it must present a less brilliant aspect.
“Briefly, the position of Halley’s comet at the return is not yet known with any decided accuracy. Cowell and Cromelin (Monthly Notice, Royal Astronomical society, Vol. 68) give the perihelion passage April 3, 1310. They are doubtless nearer it than others, but there is an uncertainty of perhaps several weeks. The largest field of view of the 40 inch telescope is less than six minutes of arc. This will be covered many times by the little fingernail held at arm’s length. The astronomer, therefore, can see but a small speck of space. If the position of an object be closely known, it can be readily picked up if bright enough to be seen in the 40 inch. But if the place is uncertain by some degrees it would be a great loss of time to hunt for it with the 40 inch.
“At the same time, the photographic plate is far more sensitive than the naked eye to the light of a comet. The field of view of a photographic telescope is far greater than that of the visual telescope so that it can readily take in, in one picture, ail the region that is likely to contain the comet. There are much greater chances of the comets being picked up with some of the reflecting telescopes, or with some of the portrait lenses, by aid of the photographic plate. Though the comet will be very faint the coming fall and winter, I have no doubt that it will be found photographically.”
The comet’s current location
The comet is now out between the orbits of Jupiter and Saturn. It will be within the distance of Jupiter’s orbit after March 1, 1909. It is possible that some one with the aid of a great telescope or photographic camera may catch sight of the expected visitor during the Winter of 1908-1909. We may begin to search for it as early as September, 1908, provided good ephemerides are at hand. Almost certainly it may be found by September or October.
It will then be only a round nebula, whatever tail it has being almost directly behind it as seen from the earth. The date of its nearest approach to the sun, according to H.C. Wilson, should be March 10, 1910.
After October, 1909, the comet will probably be visible to the unaided eye. Even now it is nearer to us than Saturn and is rushing forward at the rate of 520 miles a minute. After it passes Jupiter, the next planet on its way, the speed will increase to 783 miles a minute. It will then plunge through the zone of asteroids, or tiny planets which wander between Jupiter and Mars. Woe to any small asteroid it may encounter on the way, but worse still for the comet, should it crash head on in its mad career into the giant planet Jupiter, the great disturber of comets.