LOCATING THE STARS.

Otago Daily Times, Issue 19529, 11 July 1925, Page 9

LOCATING THE STARS.

By J. A. Lloyd, M.8.A.A., in the Daily MaiL Star-gazing fs not an easy job. Few people realise what it means to taka charge of a large astronomical telescope. A modern telescope is a gigantic affair, often 50ft or more in length and weighing 30 or 40 tons. Two or more 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 be found. This is done by means of graduated circles attached to the telescope. Knowing the Right Ascension and Declination of the star, which are given in all star catalogues and charts, the circles are set to this position. Then, if the instrument is correctly adjusted, the star will be seen in the centre of the field of view on looking through the telescope. But it will not stay there. The earth is turning on its axis; consequently the stars appear to rise and set. So the telescope must be made to follow the stars. This is done by powerful clockwork mechanism or an electric motor. The great telescope at Greenwich ■ Observatory is driven by a water-turbine. Of course, the motion must be regular, and this means great mechanical refinement in governing the speed of the motors. The observer then takes his place at the telescope. He usually has to climb up step-ladders in order to reach the eyepiece, 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 seen only in some very modem observatories. The observer often has to put up with intense cold. The 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 modem astronomy. The telescope is converted into a camera, a photographic plate taking the place of the observer. Even then the astronomer’s lot is not materially lightened. Photography only enables him to accomplish more m a given time. A field of stars can be photographed in an hour or two that would take months to chart by eye and handStill, the observer must not leave the telescope for an instant.. A 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. If this takes place, the photograph is ruined.