LOCATING THE STARS

Nelson Evening Mail, Volume LVI, 18 July 1925, Page 3

LOCATING THE STARS

By 1. A. Lloyd, M.UA.A., ill the I Oily Mail. Star-gazing is not' an easy job. bow people realise what- it. means io take charge of a. large astronomical telescope. A modern telescope is a, gigantic ■•ffiir often bOft or more in length am* weighing AO or AO t ons, l*vo - oi mol c men are, required to work such an instrument. One man is the observer proper, the others acting" as his assistants , . . , First of all. the star or other object to be observed must lie ton ltd. This is done by means of graduated circles attached ’to the. telescope. Knowing the night Ascension and Declination of t he star, which arc given in all star catalogues and charts, the circles are set t-o this position. I hen, if the instrument is correctlv adjusted, the star will be seen in the centre of the held of view on looking through the telescope. Rut. it will not, stay there. The earth is turning on its axis: consequently the, stars appear to rise and set. bo the telescope must be made to follow the stars. This is dune by powerful clockwork mechanism or an electric motor. The great telescope at Grenwieh Observatory is driven by a wafer-turbine. Of course, tlic motion must be regular, and this means groat- mechanical refiniinciit jn governing the speed of the motors. The observer then lakes his place at the telescope. ‘He usually has to climb up step-ladders itt order to reach the “vopiere though sometimes the whole floor of the observatory can be raised or lowered as desired by hydraulic power. But this is a comparatively recent invention, and is only seen in some very modern observatories. Tin* observer often has to put up with intense cold. Tin' observatory must, not be artificially heated. or it is found that the currents of warm air set up seriously interfere with the efficiency of the telescope. Since most observatories are built on high mountains, the cold is sometimes very severe indeed. Photography plays a large, part in modern astronomy. The telescope is eonverted into a camera, a. photographic plate taking the place of the observer. Even then the astronomer’s lo't, is not materially lightened. Photography only enables him to accomplish more in a given time.

A field of stars can be pi min graphed in an hour or two that would take months to chart by eye and band. Still, the observer must not leave the telescope for an instant. A smaller telescope is mounted parallel to the main instrument. Through this the astronomer watches assiduously lest the clockwork should drive the telescope too fast or too slow and cause the stars to shift on the photographic, plate. Tf this takes place, the photograph is ruined.