GLORY OF THE STARS

New Zealand Herald, Volume LXXV, Issue 23052, 1 June 1938, Page 10

GLORY OF THE STARS

HEAVENS IN JUNE EARTH AS A TIMEKEEPER CHECK ON VARIATIONS BY CBTJX AUSTRAIjIS Ever since the dawn of intelligent on this globe*'the Earth has been used as man's timepiece. Its diurnal rotation upon its axis gave us day and night, which periods were soon sub. divided into hours which varied in length with the seasons. Then came the sundial and thik hours of equal duration. Pendulums brought us mechanical clocks which functioned whether the Sun was shining or not. Gradually the standard of accuracy m clocks improved, until nowadays we have the astronomical perfection, varying only a few hundredths of a second in the course of a year. All this time mankind had implicit faith in the basis' of its timekeeping and sought to design clocks that would be as accurate as the Earth itself. Astronomers, however, had doubts. The study of ancient eclipses of the Sun and Moon, revealed that, the Earth's rotation was very gradually slowing down, doubtless due to the cumulative effects of the friction of the tides. To complicate the position, however, there were large irregular jluctuations to be accounted for in some way. New Problem Arises For many years there existed the lunar problem, as it was termed, which exercised the brains of many a mathematical genius before it was finally cleared up. When the Moon's orbit had been accurately determined, the next step was the construction of tables by which its position for many year.'t ua advance could be predicted. Hardly had the tables been published, however, than the Moon began to deviate from the position predicted for it. Sometimes it was ahead and sometimes lagging behind, but rarely was it in the correct position. This was a state of affairs astronomers could not tolerate. They blamed the accuracy of the tables and the accuracy of the orbit originally deduced. Laborious calculations were painstakingly repeated and still the errant Moon wandered from its course. The most famous mathematicians met their Waterloo on this problem. Every conceivable force which acts upon our satellite was brought into the calculations and given due weight, but with no better result. Cause of Trouble Found The Moon was not alone in this singular behaviour. The innermost planet, Mercury, also was r behaving strangely, and even when Einstein's relativity theory explained away the most of this peculiarity there still remained an annoying residual. Then, finally, the problem was elucidated. Dr. Brown, a leading mathematician of our day, discovered that the whole of the trouble was due to the irregular motion of the Earth—the partner in this unusual problem whose conduct had always regarded as above suspicion. . Small changes in the Earth's mass, such as caused by land-slides and earthquakes, immediately had their repercussions on its rate of rotation. Nowadays, to keep a check on our timepiece, the times when stars disappear behind the Moon in occultation are carefully recorded all over the world, and the information thus secured enables the astronomers to determine whether the Moon is ahead or behind in its timetable. The Transits of Mercury Another check on the slow lengthening of the terrestrial day has recently been secured by a study of the transits of Mercury. These phenomena are gradually _ running ahead of calculations just as would happen if our days were getting longer. It reveals also that tidal friction is forcing our satellite further away from us and lengthening its period. The irregular fluctuations in the Earth's rotation affect Mercury and the Moon in exactly the same manner, confirming Brown's discovery that they originate in the Earth itself. In another research the transits of the Moon across the meridian have been corrected to allow for whether a lunar mountain or valley was observed on the wire of the transit instrument, and much better agreement in timing has resulted. For several years past the Earth's rotation seems to havo been quite uniform, and there havo been no internal changes affecting its diameter by more ,than an inch or so. Phenomena for June The Sun is at present in the constellation Taurus, in which it will remain until June 21, when it will pass into Gemini. The winter solstice will occur on June 22, when the Sun will attain its lpwest noon altitude in these skies. The Moon, in the course of its monthly journey around the zodiac, will be in conjunction with the various naked-eye planets as follows: —Mercury, Ist, 3.30 a.m.; Jupiter, 19th, 2.30 p.m.; Saturn, 23rd, 2.30 a.m. The planet Mercury, at present in the morning sky, wilf pass behind the Sun on June 22, then entering the evening sky. Venus is gradually attaining a more prominent position in the north-western evening sky. Mars lies too close to the Sun for observation this month. The brilliant Jupiter, which now rises at midnight, is attaining a more favourable position for observation, while the more distant planet Saturn is also visible only after midnight.