SUN'S ECLIPSE

Wanganui Chronicle, Volume 79, Issue 64, 16 March 1936, Page 10

SUN'S ECLIPSE

INTERESTING PHENOMENON VISIBLE NEXT DECEMBER, VANTAGE I’ol NTS IN AUCKLAND PROVINCE. Of the many interesting astronomical phenomena predicted to take place during this year, none will capture the interest of the people of New Zealand more than the annular eclipse of the sun which is predicted to occur on December 14 next, writes the “Chronicle’s” astronomical writer. Eclipses, both solar and lunar, are rot rare phenomena by any means, but it is seldom that a total or an annular eclipse is visible in this country, and accordingly, astronomers and others interested are making the best use of the opportunity' presented to them. Solar eclipses up till recent times, have always been regarded as of great , importance from the fact that the sun, the giver of light and the sustainer of life, appears to be swallowed up by some unknown agent, and the need of the moment is to beat off the swallower. In China the most important duty of the ancient astronomers was to predict the eclipses, and a mistake in calculation meant execution for the unhappy astronomers-royal. One of the most famous eclipses of antiquity is that recorded by Herodotus who records: I “The hydrians and the nedes were I at war for five consecutive years. While the war was sustained on both sides by equal chance, one day in the sixth year, when the armies were in battle array it happened that in the midst of the conflict the day was suddenly changed into night. Ihales of j Niletus had predicted this pheno- | menon to the lonians, and had pointed out precisely that very year as the one in which it would take place. The ll.ydians and the Nedes, seeing the night succeeding suddenly to the day, put an end to the combat, and only cared to establish peace.” Ihales, born about 640 B.C. in the Greek Colony of Niletus on the coast of Asia Minor, was one of the first thinkers to turn the minds of the lonian Greeks from superstitious fantasies to a fearless inquiry into the ways of nature. He it was who first made it known to the Greek world that a solar eclipse was caused by the interposition of the moon between the sun and the earth. Ihales concluded from this that the moon was a dark body that shone by reflected sunlight. Ilf successfully predicted the eclipse of May 28, 585 8.C., which is the one mentioned above. If the moon and the earth moved in the same plane we should have two eclipses each month: a solar eclipse at new moon and a lunar eclipse at full moon. As the moon moves in an orbit inclined at an angle of sdeg. 9min. to the plane of the earth’s orbit, there can be no eclipse either a new or at full I moon unless the centre of the moon is ( within an angular distance of 30min. | from the plane of the ecliptic. In gen- | eral the moon will pass either over or under the cone joining the sun and the earth. The Chaldeans discovered that

after a. certain lapse of time from an eclipse, the sun, moon and the earth return to almost exactly the same positions and an eclipse similar to the prior one again takes place. This period is known as the Saros, and amounts Io 6585 days, or 18 years II days if onlyfour leaps years intervene and .18 years 10 days if February 29 occurs five times. Eclipses, therefore, occur in cycles, and it is possible to trace the conditions of each eclipse of the series. The average length of the shadow of the moon is about one four-hundredth of its distance from the sun and at new moon is 232,100 miles. Since the length of the shadow is less than the mean distance of the earth from the moon (238,000 miles) on the average the shadow will not touch the earth. The moon’s orbit is not circular and for much of the time the moon is within 232,000 miles of the earth, when its shadow, if eclipse conditions prevail, will touch the earth and the sun is then totally eclipsed. If the shadow does not touch the earth, the sun is not completely obscured, and a small ring of light may be seen surrounding the disk of the moon. This type of eclipse i« called “annular” (from the Latin word annulus—a ring) and this is the type of eclipse which will be visible in December next. The eclipse generally will be visible in Australia and neighbouring islands, and over a large part of the South Pacific and Antarctic Oceans. The patch of aunularity begins on the ocean between Java and the north-western coast of Australia, strikes the coast at Broome, crosses the continent in a south-easterly direction, passing off the eastern coast about 200 miles , north of Sydney; passes easterly over the Auckland province and ends in mid-ocean without touching any of the small islands in the Pacific except the island Teno, about 100 miles north of Pitcairn. The eclipse will be visible as an annular one throughout the greater part of the Auckland province, the northern limit being a line running approximately through Dargaville and Great Barrier Island and the southern limit a line through Piopio and Morere Hot Springs, south of Gisborne. All places within these limits will see the eclipse as an annular one. The sun at Auckland will be eclipsed for about seven minutes. Throughout the rest of New Zealand th® sun will be partially eclipsed, the phase varying with the distance of the observer from the central path of the eclipse. At Wanganui, about .88 of the sun’s disk will be obscured by the moon, so a really interesting spectacle can be looked forward to by all interested. The eclipse will commence about half-past nine and finish about three hours later, the greatest phase taking place at eleven o’clock. Anyone, provided the weather is clear, can view the progress of the moon across the sun’s disk, with the aid of a smoked piece of glass—direct observation with the eyes unprotected being dangerous to the eyesight. Partial eclipses are not of great interest from a scientific point of view, but by observing the exact time of contact of the moon’s shadow with the sun’s disk, the position of the moon, whose vagaries are the despair of the scientist, can be checked with the predicted position.