GLORY OF THE STARS

New Zealand Herald, Volume LXXII, Issue 22149, 1 July 1935, Page 6

GLORY OF THE STARS

HEAVENS IN JULY If PLANETS AND POSITIONS 1 , - CONSTRUCTION OF TELESCOPES BY CRUX AUSTIIALIS The great Hooker telescope on the summit of Mount Wilson in is the largest" instrument at present use in the world. It is a reflector, the light rays from the stars being gathered in by a huge parabolic mirror, which; reflects them to a focus, where they are examined by magnifying eyepieces. The 100-inch diameter mirror was distinct gain in size on the previouj best, a 60-inch mirror situated at the same observatory. The delays and mishaps accompanying the casting and an. nealing of the huge glass disc weighing 4i tons caused astronomers to believe that the practical limit had been reached in the construction of these tremendous instruments. Apart fro® the shaping of the glass to the requisite curve, a long and arduous task, the on. gineers found a task to tax their ability in designing a mounting which would support moving parts weighing 100 tona and yet permit of this huge weight, being moved smoothly and accurately in following the motions of the stars. Two Hundred-Inch Mirror Another large bequest recently be. 1 came available to «he Californian Institute of Technology for a 200-ittch mirror and the making of a gla&j disc was entrusted to an American firm, the Corning Glass Works. Ons disc was poured, but in the process some of the pylous: used to produce a honeycomb structure on the back of the disc broke loose and floated to the surface. It is believed, however, that the glass will still be usable, and the work of cooling the disc, a viery slow process, was continued. In case the first disc had been spoiled by this accident, the casting of a second 200-inch mirror was performed toward the end of last year, being a perfect success, and the Californian Institute of Technology ij now in possession of two 200-inch discs of pyrex. ■ '■■W From the experience gained, the glass company believes it could make much larger discs if necessary; certainly ons of 300 inches or even .400 inches p within its capabilities. Tile practiaf limit, so far as the casting goes, thes. fore* has not nearly been reached.

Kange of Instrument It is expected that with the new tek scope it will be possible to photograph stars of the 25th magnitude, with an intensity of light only one-fifteenth of the faintest it is possible to photograph with the 100-inch mirror. Not only will astronomers be able to plumb further into the depths of space, but also fresh details of known objects will be revealed. It has been decided to erect the ner telescope at Mount Palomar, San Diego, about 100 miles south of Pasadena, California, where tests have revealed aneminently suitable site for such a tiamendous instrument. In a recent lecture the Astrom<mw Royal stated that preliminary designs for a 300 in. reflecting telescope had been prepared by one of the astronomers tt Mount Wilson Observatory. The mirrtr would have a diameter of 25ft., whi'e the instrument would Ibe over 80ft. in length. Its moving parts are estimate to weigh about 1600 tons. 2j. The cost of constructing and settttt up the lOOin. Hooker telescope was ever half a million pounds, whiie it is esimated that two million pounds will .j expended on the 200 in. instrument, jjl the attempt is ever made to constrtrf the 300 in. mirror a tremendous finaneii outlay will be entailed, and possibly ttf financial limit to the construction if telescopes may be reached long befm the practical limit is attained. Phenomena for July |j[v The Sun will be in the constellatiffl Gemini until July 20, when it will pjiss into Cancer. It is now slowly risiiis higher in the sky, its noon altitude si Auckland increasing from 30deg. to 35deg. during the month. A partiil eclipse of the Sun will occur on July 18. but this can be observed only from Antarctic regions. The Moon will be in conjunction witl the various planets as follows: —Venus, sth, 11.30 a.m.; Mars, 9th, 9.30 p.nt; Jupiter, 11th, 6.30 p.m.; Saturn, 20th, 12.30 p.m.; Mercury, 29th, 5.30 p.m. A total eclipse of the Moon will oceat on July 16, the Moon rising in New Zealand as th? final penumbral stage is taking place. Mercury will attain its neatest elongation in the morning sky on the 14th. Venus remains a brilliant object in the north-western evening sky. It attains its maximum brilliance at the end of the month. Mars is now becoming too distant for telescopic study, although it is still prominent to the naked eye in the evening sky. Jupiter is well situated for observation, and the many interesting changes which are occurring on its cloud-covered surface provide subjects for study by telescopists. Saturn is prominent now in the morning sky.