\E`qua*to"ri*al\, a. [Cf. F. ['e]quatorial.]
Of or pertaining to the equator; as, equatorial climates;
also, pertaining to an equatorial instrument.

\E`qua*to"ri*al\, n. (Astron.)
An instrument consisting of a telescope so mounted as to have
two axes of motion at right angles to each other, one of them
parallel to the axis of the earth, and each carrying a
graduated circle, the one for measuring declination, and the
other right ascension, or the hour angle, so that the
telescope may be directed, even in the daytime, to any star
or other object whose right ascension and declination are
known. The motion in right ascension is sometimes
communicated by clockwork, so as to keep the object
constantly in the field of the telescope. Called also an
{equatorial telescope}.
Note: The term equatorial, or equatorial instrument, is
      sometimes applied to any astronomical instrument which
      has its principal axis of rotation parallel to the axis
      of the earth.