IN STARRY SKIES

Evening Post, Volume CIX, Issue 44, 21 February 1930, Page 15

IN STARRY SKIES

.. .■■- ■'•—?. *-r- —-v- ■--..■•: THE FILAMENTOUS NEBULA IN CYGNUS

(By "Omega, Contauri.")

This photograph gives another fine example of the stage reached by Professor-. G. W. Kitchey, nearly twenty years ago, in the photography of faint objects in the heavens. It shows a part only of the wonderful gaseous iiobula known as N.G.C. 6960. Tho field shown is about 25 minutes by 30 minutoSj^the greatest length being about equal to the diameter of tho moon. This nebula and its neighbour, N.G.C. 6992, are believed to be parts of, a. vast cloud,- of which portions: :-only ■', are. illuminated. But the source of the lumination is ail unsolved; ; problem. Hubble finds that,, with tho. exception of this; associated pair*, every : iuniinous. diffuse uebula surrounds,!or lies near, to, "a conspicuous star, which is usually of .a spectral type indicating an extremely hot surface. No star sufficiently brilliaut appears here. ■■ The brightest shown in the photograph' is only iof the sixth magnitude. It has' been/ suggested, however, that one may be hidden by unusually opaque nebulosity.- That dark matter is abundant in the vicinity is clear from the striking 'difference-in the number, of stars

seen on the . two sides •: of :• the bright nebula. .Wlren a nebula is'definitely associated with a star, it is usually possible to find its distance from us. Tho diffused nebulae seen to lie at distances ranging from 326 to 650,000 light years. "Shis nebula is approaching us at about twelve miles a second, whilst its companion is receding at about 03 miles a second. This, difference may bo due to the rotation of the whole vast mass, of which the bright nobulae arc merely the illuminated edges. But this tremendous mass is not only rotating, . but is apparently expanding also. Proper motion, at the. rate of one second in twenty years, has been detected. In Eu,6sell, Dugan, and Stewart's Astronomy, the suggestion is made that thY nebulosity may possibly have been expelled, from a gigantic nova... .100,000 yeaTS cago. This idea is advanced only as a tempting speculation, but again1 wb think of the leveiatio'ns that may be expected when Hitch ey turns on to this object ono of his supor : giant. telescopes. This photogiaphwas.taken with the. 60-inch Mount Wilson reflector on the nights of 4th and sth July, 1910. The exposure was 0] hours.. Long before that, when Bitchey had* just completed liis first 24-inch mirror, he had already conceived the idea, which ho is'-jtow carrying into effect, of building up enormous mirrors out of plates'of pyrcx or fused quartz. He had also formulated" the problems on which he has ■ been .working ever since. He realised, tij^ possibility of calculating new curves for tho mirrors, so as to secure more concentrated images. lie knew that''iphotographie plates must be greatly'improved, and he embarked in

researches wfcich have been crowned with astonishing success. Ho saw that, to. make. : a. perfect instrument, .. every detail of .the mounting ventilation and housing must bo made the subject of a thorough investigation. Ho had faith in the possibility of making hugo reflectors at a time when most astronomers wero convinced that tho limiting diameter was about 3G inches. "Demonstrate," lie said, "tho •practicability of it. Write articles and. booksior it; lecture. for-,.it;. argiio for it; plead for it.. Fight for it. the opposition of reactibnarics. Interest' millions of the best men and women in it; and in this generation, we. shall attain it. It will repay ua. immeasurably for all our efforts; for ,our lifelong devotion.'' ' Tliesq aro inspiring words, v and Kittrfiey'has accomplished .a ; , great part of: what'he set'out to. do. \:Caunot we now join .'in and do our'-little bit. ' If a million people in New' Zealand can be stirred to take even the interest iii astronomy, we shall be'able to . securo an. instrument 'of the newest type/and to build and-endow a People's Observatory. ' ..;..-

.". By using many plates, instead of one colossal disc, Bitehey has not only, reduced the initial cost, but has solved also.the transport problem. The plates.can:bc carried separately to the select-, eel mountain top,, and tho cementation and figuring can be done there. The fundamental' problem, Bitohey points out, is"to support in perfect optical foiftn a film "of silver weighing only a very small, fraction of an.ounce.. Why use a. single- piece of glass weighing 16,000 pounds, especially, as the difficulties ;in the.waj. of. its production and its cost

are: both prohibitive?

. •'?' Another great- advantage of the com-' posite disc is that it makes possible an efficient system of forced ventilation which still further minimises any deleterious effects of chaugo of temperature. The" buildings'that have been designed to hold tho new instruments are similarly protected". Tho telescope and all its accessories are in a massive inner concrete bnjlding, whilst the dome is carried by an outer structure. built of seeel," the whole being further sheltered by a light sun-shield of plate steel.' The observatory, which is to hold a smetre fixed.universal telescope, has five stories besides the dome. Two of these are below-the level of the ground, the bottom: floor being at a depth of 59 feefc: The. total height from the ground to tho top,of the dome is 174 feet. By Tising/'four large concave mirrors, and live:small secondary mirrors, a systftn. .has'been de-vised which enables tho .'directive--focal'.length of the instrument .to.ibV" changed, and all the: apparatus completely readjusted in four minutes. The following focal lengths are available, 45, 66, 102, 108, and' r o3o feet. Photographic attachments, ; arid;., all kinds of■ astrophysieal apparatus,' can' be run into -position7 along, horizontal rails on■: the lowest, floor :.-59 feet below the .surface of the ground: These telescopes are intended ,to work through only forty degrees of declination. Hence it. will; be -necessary to place them in. different latitudes, so as to command the full sky. One placed, for instance, in Central Otago,. would do its best work on the zorie:froni .25 to. 65. degrees, of South Declination. \ ' ; .t"