THE MOON’S VARIATION

Evening Star, Issue 20053, 19 December 1928, Page 10

THE MOON’S VARIATION

CAINS AND LOSSES IN LAST TWO CENTURIES !?ir Frank Dyson, the Astronomer Itoynl, addressing (lie British Horological Institute, London, recently, on ‘Astronomical -Measurements of Time,’ told of errors in the rotation lime of tber earth and moon (reports the ‘ Mundicsfcr Guardian '). In about two centuries, ho said, the moon had never been more than one twohundredth parts of its diameter ahead or behind its predicted date.' This was worked out by Nowcombc, and the result summarised by Professor Be Siller went to show that about 1650 (ho moon was 30sce slow on astronomical time. It licgan to gain about 1670, and by 1720 had made up tho arrears. By 1755 it. was nearly 30sec ahead, and then started to lose again, and was back to the time of tho rotating earth by 1865. Then it got more and more behind (ill about 1900, when it slarfed to gain once more, and it was about 18sec Irehind in 1918, when once more it Marled to lose. From 1876 to 1897 tho moon Inst ISscc, and from 1897 (o 1918 gained llscc. The sun also lost, and then gained, according to Do Siltor, 19seo and Msec; but it could not, bo said that the change, about 1918 shown by (.ho moon was also shown by t.ns sun. “ Can the, horclogisls help the astronomers in this important problem*?'' asked Sir Frank Dyson. “ What, we, should like is half a. dozen clocks in the, best oliscrvalories which could bo trusted to keep lime to one second a year. Ido not, despair of a good enough clock to check the ditlcrences astronomers find in Ihe celestial timekeepers,” he added.