HALLEY’S COMET

Sun (Auckland), Volume III, Issue 886, 1 February 1930, Page 6

HALLEY’S COMET

STORY OF ASTRONOMER WORK FOR SCIENCE The name of Edmund Halley has become a household word through the famous comet, Halley’s Comet, as it it now called, whose return he has predicted. Though this is not Halley’s chief claim to fame—for he was a very remarkable man —the story is an interesting one. A bright comet had appeared in the year 1682, when Halley was 26 years old. Observations had been duly made, and Halley was using these to calculate the orbit of the comit, using Newton’s theory as a basis. Some 50 years earlier the great astronomer Kepler, as a result of a study of the motions of the planets which had extended over more than a score of years, had formulated three laws which he had proved to be true. It then occurred to Halley to calculate the elements of the comet which Kepler and other astronomers had observed in 1607, of which records were available. Newton’s theory gave elements for the orbit which were in close agreement with those of the comet of 1682. Not yet completely satisfied, he obtained with some difficulty a book by Apian in which was given an account of a comet seen in 1531, and recording some observations. Halley again used Newton’s theory to derive the orbit of Apian’s comet, and found it to agree with the orbits of the comets of 1607 and 1682. He concluded that the three comets were one and the same, and committed himself to a prophecy, which could not be checked for 53 years to come, and which, being then 49 years of age, it was very unlikely that he would himself see fulfilled. This was that the comet would return about the end of the year 1758, or early in the following year. He left his conclusion “to be discussed by the care of posterity, after the truth is found out by the event.” He concludes with the following words: “Wherefore if, according to what we have already said, it should return again about the same year 1758, candid posterity will not refuse to acknowledge that this was first discovered by an Engiisman.” Halley died on January 14, 1742, and the comet which now bears his name was seen again- On Christmas Day, 1758, in accordance with his prediction. The comet was seen again in 1835, and many of the readers of this article will recall its last appearance in the year 1910. His Work at St. Helena Halley has other claim to remembrance. He was the first to make astronomical observations in the Southern Hemisphere. Tycho’s places for the northern stars were defective enough, judged by modern standards, but there were no catalogues at all of stars which could not be seen from Tycho’s observatory. Halley was so been to enter this unworked field that he would not wait at Oxford to complete his degree, but at the age of 21 he left England for St. Helena, and there, in the years 167678, he laid the foundations of stellar astronomy for the Southern Hemisphere. The choice of station was not a happy one, on account of the prevalence of clouds, but he succeeded in making a catalogue of 341 stars, which was later published by Flamsteed, the first astronomer royal, at the Royal Observatory, Greenwich, whom Halley was later to succeed, in “Historic Coelestis.” Another interest of Halley’s was the behaviour of the magnetic compass and its variations. He was given a captain’s commission in the Royal Navy by King William 111., and placed in command of a small vessel named the Paramour, in which he proceeded to the southern seas. This seems to have been the first organised scientific expedition, apart from journeys of discovery. Halley sailed as far as latitude 52deg. south, studied the tides and the behaviour of the compass, and as a result of the voyage produced a chart of the Atlantic Ocean, together with the first magnetic chart ever to be published—showing the deviation of the compass at any point. No navigator would now think of starting upon a voyage without t» reliable magnetic chart. Halley also, on this voyage, devised the principle of the sextant, now universally used by the navigator for fixing his latitude at sea. When Flamsteed died in 1720, Halley was his obvious successor as Astronomer Royal. The position at Greenwich was discouraging. Flamsteed’s salary had been £IOO a year, out of which he had to provide such instruments as he required. When he died, his widow removed the instruments, and Halley, at the age of 64. had practically to begin afresh. He succeeded in getting a grant for instruments, and equipped the observatory as well as was possible at the time, and then embarked upon a series of observations of the position of the moon through the period of a saros—the period of IS years, 10 days, which brings the sun and moon very nearly back again into the same positions relatively to the earth. These positions w-ere required for the construction of more accurate tables of the moon than were then available. It was an ambitious scheme for a man over 60 years of age to embark upon, but Halley managed to carry it through to success. He was one of the true servants of science, free from self-seeking, generous by nature, and a loyal friend.