Equatorial

Equatorial, in Astronomy, is a telescope designed and arranged for special observations. The telescope itself is capable of rotating at right angles about one axis, and this again may be rotated about a second at right angles to the first. The first is called the declination axis, and the second the polar; the latter is fixed in position so as to point to the poles. Rotation of the telescope about the declination axis commands a view along a meridian. If clamped to this axis and rotated about the polar axis, it views points on parallels of declination, all these points being at the same distance from the pole. Such a parallel is the path of a star or planet, and if the polar axis is rotated at the proper rate by clockwork, the telescope may be made to "follow" the object viewed. Equatorials are the most convenient in this latter respect, and also for finding objects from the usual data of declination and right ascension. The largest telescopes are therefore built with the equatorial mount, as, for example, the 23-inch Clark telescope at Princeton, the 4-foot Melbourne reflector, and the great 36-inch Lick reflector in California. [Telescope.]