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1. of, like, or existing at or near the equator
2. Astronomy of or referring to the celestial equator



a lens or mirror telescope on a parallactic, or equatorial, mounting (seeTELESCOPE MOUNTING). A clock mechanism rotates the telescope around a polar axis at a rate of one rotation per 24 sidereal hours, so that the celestial object being observed, which moves because of the apparent diurnal rotation of the celestial sphere, remains in the field of view of the telescope. Graduated circles with measuring devices are secured to the axes to direct the telescope at the celestial object according to its hour angle and declination and to enable the approximate determination of its coordinates. Auxiliary astronomical tubes mounted on the primary one, called the finder and the guide, are used to locate the necesssary object and to keep the instrument directed at it during photography.

Equatorials may be visual (equipped with an ocular that has a micrometer for differential measurements) or photographic (with plateholders). (SeeASTRONOMICAL INSTRUMENTS AND DEVICES.)

References in periodicals archive ?
On this night Ainslie employed his 9-inch silvered reflector, on an altazimuth stand, up to one hour past local midnight (x180, x270 and x400) and then used an equatorially mounted 81/2-inch (216mm) reflector by Calver (x170 and x250) which he seemed to possess at that time.
The Centre has two telescopes--an 11-inch Dobsonian donated by Dudley Field and a 13-inch equatorially fork mounted Newtonian reflector built and donated by club member Steve Kleyn.
Hay owned a number of telescopes at Norbury, but the largest instruments were his 12 1/2-inch (318mm) equatorially mounted f/7.
Finding the 10" telescope too cumbersome, Peter decided to make an equatorially mounted 6" reflector from scratch including grinding his own mirror.