From calculations on the orbit of Halley’s comet, the next return of which is due in 1910, Messrs. Cowell and Crommelin find that the identity of the comet shown on the Bayeux Tapestry with Halley’s comet is now “fully established.” They find that the date of perihelion passage was March 25, 1066, which differs by only 4 days from the date found by Hind. The imposing aspect of the comet in 1066 described in European chronicles of that time is confirmed by the Chinese Annals. In the latter records the brightness is compared to that of Venus, and even with that of the moon! The comparison with the moon was probably an exaggeration, but the comet doubtless made a very brilliant show. In the Bayeux Tapestry the inscription on the wall behind the spectators reads: “isti mirant stella.” Now, this is bad Latin, and Mr. W. T. Lynn has made the interesting suggestion that some of the letters are hidden by the buildings in front and that the real sentence is “isti mirantur stellam.”[202] The present writer has examined the copy of the Bayeux Tapestry which is in the Dublin Museum, and thinks that Mr. Lynn’s suggestion seems very plausible. But the last letter of stellam is apparently hidden by the comet’s tail, which does not seem very probable!
The conditions under which the comet will appear in 1910 are not unlike those of 1066 and 1145. “In each year the comet was discovered as a morning star, then lost in the sun’s rays; on its emergence it was near the earth and moved with great rapidity, finally becoming stationary in the neighbourhood of Hydra, where it was lost to view.”[203] In 1910 it will probably be an evening star before March 17, and after May 11, making a near approach to the earth about May 12. About this time its apparent motion in the sky will be very rapid. As, however, periodical comets—such as Halley’s—seem to become fainter at each return, great expectations with reference to its appearance in 1910 should not be indulged in.
The appearance of Halley’s comet in A.D. 1222 is thus described by Pingré—a great authority on comets—(quoting from an ancient writer)—
“In autumn, that is to say in the months of August and September, a star of the first magnitude was seen, very red, and accompanied by a great tail which extended towards the top of the sky in the form of a cone extremely pointed. It appeared to be very near the earth. It was observed (at first?) near the place of the setting sun in the month of December.”
With reference to its appearance in the year 1456, when it was of “vivid brightness,” and had a tail of 60° in length, Admiral Smyth says,[204] “To its malign influence were imputed the rapid successes of Mahomet II., which then threatened all Christendom. The general alarm was greatly aggravated by the conduct of Pope Callixtus III., who, though otherwise a man of abilities, was a poor astronomer; for that pontiff daily ordered the church bells to be rung at noon-tide, extra Ave-Marias to be repeated, and a special protest and excommunication was composed, exorcising equally the Devil, the Turks, and the comet.” With reference to this story, Mr. G. F. Chambers points out[205] that it is probably based on a passage in Platina’s Vitæ Pontificum. But in this passage there is no mention made of excommunication or exorcism, so that the story, which has long been current, is probably mythical. In confirmation of this view, the Rev. W. F. Rigge has shown conclusively[206] that no bull was ever issued by Pope Callixtus III. containing a reference to any comet. The story would therefore seem to be absolutely without foundation, and should be consigned to the limbo of all such baseless myths.
With reference to the appearance of Halley’s comet, at his last return in 1835, Sir John Herschel, who observed it at the Cape of Good Hope, says—
“Among the innumerable stars of all magnitudes, from the ninth downwards, which at various times were seen through it, and some extremely near to the nucleus (though not exactly on it) there never appeared the least ground for presuming any extinction of their light in traversing it. Very minute stars indeed, on entering its brightest portions, were obliterated, as they would have been by an equal illumination of the field of view; but stars which before their entry appeared bright enough to bear that degree of illumination, were in no case, so far as I could judge, affected to a greater extent than they would have been by so much lamp-light artificially introduced.”[207]
It is computed by Prof. J. Holetschak that, early in October, 1909, Halley’s comet should have the brightness of a star of about 14½ magnitude.[208] It should then—if not detected before—be discoverable with some of the large telescopes now available.
According to the computations of Messrs. Cowell and Crommelin, the comet should enter Pisces from Aries in January, 1910. “Travelling westward towards the star γ Piscium until the beginning of May, and then turning eastward again, it will travel back through the constellations Cetus, Orion, Monoceros, Hydra, and Sextans.” From this it seems that observers in the southern hemisphere will have a better view of the comet than those in northern latitudes. The computed brightness varies from 1 on January 2, 1910, to 1112 on May 10. But the actual brightness of a comet does not always agree with theory. It is sometimes brighter than calculation would indicate.
According to Prof. O. C. Wendell, Halley’s comet will, on May 12, 1910, approach the earth’s orbit within 4·6 millions of miles; and he thinks that possibly the earth may “encounter some meteors,” which are presumably connected with the comet. He has computed the “radiant point” of these meteors (that is, the point from which they appear to come), and finds its position to be R.A. 22h 42m·9, Decl. N. 1° 18′. This point lies a little south-west of the star β Piscium.