Halley's Comet. (After H. C. Wilson IN Popular Astronomy.)

Progress, Volume IV, Issue 2, 1 December 1908, Page 64

Halley's Comet. (After H. C. Wilson IN Popular Astronomy.)

In ancient times the appearance of comets filled the people with terror and ''with fear of change perplexed monarchs." In England the most noted and the most terrifying of the whole series that disquieted the nation, during fourteen centuries was the Comet of April, 1066. None, on the othei hand, seemed to the popular mind so amply justified as a prophet of evil. Having at the beginning of the year perplexed the brave Saxon King Harold with fear of change, and flown away out of sight, the end of the year brought justification with the decisive battle of the Norman conquest. This true prophet of old time has since been identified as Halley's comet. It was seen in the fifth and eighth centuries of the Christian era, but not honoured by the usual calculations. But its third appearance and its sequel, the Battle of Hastings, prevented men from forgetting its existence. Since then it has been proved to have a period of between 74y 2 and 79 years, having returned to the neighbourhood of the Sun ten times during the seven centuries. "The question now arises," writes Professor Wilson in Popular Astronomy, "will the next return be in favourable or unfavourable circumstances'? Shall we expect to see a great magnificent comet, as in 1066 or 1456, or an insignificant object as in 1607 ? In order to aid in answering this question, I have gathered together the elements of the comet's orbit at the different apparitions which have been observed, and have drawn the consequential diagram," which we produce on this page of the present issue.

The diagram was prepared b\ the aid ol" ephemerides of the comet computed by Mr. P. E. Seagrave, of Providence, R. 1., and the elements differ slightly from those given in the last line of the table, but not enough to affect the shape of the diagram appreciably. Mr. Seagrave adopts May 10th for the date when the comet will be at perihelion. The computations of Messrs Cowell and Crommelin point to an earlier date, probably about April 8 for perihelion passage. Comparing this with the dates

in the table we see that this coincides very closely with that for the apparition in 1066 when the comet was a famous object. Now as to the 1910 apparition. The comet is now out between the orbits of Jupiter and Saturn. It will be within the distance of Jupiter's orbit after March Ist, 1909. It is possible that some one with the aid of a great telescope or a photographic camera may catch sight of the expected visitor during the winter of 1908-9. We may begin to search for it as early as September, 1908, provided that good ephemerides are at hand. Almost certainly it may be found by September or October, 1909. It will then be only a round nebula, whatever tail it has being almost directly behind it as seen from the

earth. If the date of perihelion should he May 10, the comet Mill be lost behind the sun in the early part of April, reappearing in the morning sky about the first day of May. It should reach its greatest brilliancy in the last days of May but the morning dawn will prevent its having the most striking effect. It will pass between the earth and the sun about June 1, and there is a possibility then of the tail extending so far out over the earth that it may be very conspicuous in spite of the deep twilight in which the head of the comet must be observed. After June first the comet should be visible in the evening in the western sky, a more or less splendid object according as the effect of the lessening twilight or the increasing distance of the comet be the more important factor in changing its brilliancy.

a 2^3 «S 2 2 q « ffl 53 t "'&r2& -" S"w * rt " ® m ~ tn »«O- 300 So"3 -3-2 Si 12 a l §s fl fsS II {Li -ij «3 o 1-3^ 3 *" (^ 4^ O De^reeb Degrees Degiees 451 July 3. ..108 5 53 3 16 0.62 760 June 11 ... 107.5 52.5 17 0 60 1066 Apr 1 1145 Apr. 29 1222 Sept. 15 ... 105 6 516 16 5 0.67 1301 Oct. 22 1378 Nov. 8 ... 107.77 54 67 17 9 0.584 1456 June 8 ... 104 82 50 08 17 62 0 581 1531 Aug. 25 ... 104.30 50 77 17 00 0 579 1607 Oct. 27 ... 107.25 52.66 17 14 0 585 1682 Sept. 14 ... 109.26 54 35 17 76 0 583 1759 Mai. 12 ... 110.65 55.92 17 62 0 585 1835 Nov. 16 ... 110.64 56 19 17 7b 0 586 1910 Ma) 10 ... 11l 54 57.18 17 78 059 3 % 5 79.1 77.4 79.1 77.C 77. r i 75 i 76$ 74 i 78 I 76 -3 74 ! Motion retrogiaile.

Approximate elements op Halle y's Comet reduced to the equinox of 1910.