Observing the Eclipse.

Hokitika Guardian, 11 July 1922, Page 4

Observing the Eclipse.

WOI?LD-WIDF INTEREST

THKOUY OF JSJSI..ATI VITV. j

Elaborate preparations arc being made by seientilie bodies lor the observation of the total eclipse of the sun that will occur on September 21st. The . path of totality will begin its course in Hast Africa, on the, Somaliland coast, where the sun will rise in total eclipse, and will cross the Indian Ocean, to the north-west coast of Australia, and end in tho Pnclic Ocean, north of New Zealand. A partial eclipse will be visible from New Zealand just before sunset. This will be the first total eclipse visible in Australia since its colonisation. The shadow of the moon will touch the north-west coast of Western | Australia about noon at Wallnl, and will pass the eastern coast about 2 1 p.m. at l.ixmore, in northern New South Wales. The shadow thrown from interposition of the moon between the sun and earth will ho about 111 miles wide. But far north and south of the eclipse will be seen to varying degrees of partiality, according to distance on either side of the shadow. Observers from the United States and Canada are to establish themselves at Wallal with Western Australian astronomers. The South Australian Government is to send an expedition to Cordillo Downs station, in Central Australia—a remote spot that can he reached only by weeks of travel with camels. New South Wales and Queensland observers are to operate at Oondiwindi. An expedition organised by the New South Wales branch of tho British Astronomical Society, under the leadership oi Mr W. ]•'. dale, the president, will proceed to Stanhope. OBSKHYEUS AT CIIHIST.MAS ISLAND. An expedition from the tlreecinvich Observatory, under Mr Spencer Jones, is to conduct its observations Irom Christmas Island, south of .Java, where it has already arrived. One of the. most interesting tasks,to be undertaken by tile Christmas Island expedition is to " test Dr En-toin’s theory that when a ray of light passes near matter its path becomes bent. The amount of this bending is so small that the only body which can he used to test it is the sun, whose mass is :otl times that of our earth. A ray of light lrmn a star passing near the edge of the sun is belli, and this bending is revealed to us hv an apparent displacement of the star away 1 from the edge of the sun. But the

light Irani tin l sum is so intense comImrod with that from tlio -stars that it IS hopeless to attempt to photograph stars near the sun in full daylight; this only heroines possible "’hen the light of' tlio sun is obscured hv the mooli during nn eclipse of the sum. The displaooMient of the star-images is detected by comparing the photo graphs of tin same region of the sky obtained at mip.ht about three el l»ur M.ojiths earlier. The images of the stars near the son ill the el lipse photographs "ill he (lisplneecl hy tiliont one om-two-thousandth part of an inch as min,);,red wii It their positions on the earlier plates. It is upon the mcasurenieut of siii'h small displacements that Einstein's theory, with its new mews a s to spats* and time hangs or la.ls I J!ut the. refinement of modern astronomieal measurement is cqrtal to the o - easion.