MOUNTED AT KELBURNE.

Dominion, Volume 6, Issue 1560, 2 October 1912, Page 7

MOUNTED AT KELBURNE.

THE EQUATORIAL TELESCOPE. Interest in astronomy in Wellington hae been quickened lately by the development of the Government limo Observatory, the mounting of an equatorial telescope at Kolburne, and the building of an observatory at Wellington College. The question is frequently asked, "What is an equatorial telescope?" It is simply an astronomical relescopo mounted in such, a way as to overcome Oβ far as possible the difficulties presented to an observer by the fact that all lite heavenly bodies appear in constant motion. If one looks at tho heavens through a fixed telescope, any star in sight mover rapidly across the held of view and disappears. The problem is how to mount a telescope so that the astronomer may be able, by soino simple and easily controlled motion, to follow tho star in its course. This has been achieved by mounting the tele, scope cquatoruilly. The essential leature of an oquatorhl telescope is that it can turn around nn axis which is parallel to the axis of the earth. This is called tho polar axis. When tho instrument is turned around this axis it traces out cuivos in the sky which are identical with those described by the stars in their apparent diurinl motion. If then tho telescope be directed to a heavenly body it can be made to follow tho object and keep it in view by a single movement of rotation around tho polar axis, which may bo furnished by clockwork. An equatorial has motion of rotation round another axis which is at right angles to the polar axis, and is called the declination axis. Another important feature of an equatorial telescope is that it can bo provided with graduated circles which enable the observer to point the instrument to any desirod object of known right, ascension and declination. Tho right ascension of a heavenly body, which corresponds to terrestrial longitude, is its angular distance, usually measured in hours, minutes and seconds of tune, from a point in the heavens called the First Point of Aries; the declination of a heavenly body which corresponds to terrestrial latitude, is its angular distance north or south of the celestial equator. Ono of these circles is the declination circle attached to the declination axis. It ia adjusted so as to read Odeg., when the telescope points to any part of the celestial equator, and OOdeg. when it is directed to the Pole. The other circK which is called the hour circle, is attachc<l to tho polnr axis, and determines the position of tho teiescopn with regard o tho meridian. Haying given tho right ascension and declination of a heavenly body which it is desired to observe, tho tolesoopo is turned on its declination axis until the declination circle vends, the proper angle, and on its polar axis until the hour circle indicates the proper hour anglo '(which is the difference between the right ascension of tha object and the sidereal tiinoof observation). In this way it is easy to find objects of known position which arc invisible to tho naked eve, and ono can even picii up the planets aiid bright stars in full sunshine. Converscly ouo can determine from tho circles tho right ascension and declination of any object under observation.