circle of equal altitude

A circle on the surface of the earth, on every point of which the altitude of a given celestial body is the same at a given instant; the pole of this circle is the geographical position of the body, and the great-circle distance from this pole to the circle is the zenith distance of the body.

Related terms:

• primary great circle
• secondary great circle
• great circle
• great-circle direction
• principal vertical circle
• corrected altitude
• small circle
• inertial circle
• secondary circle
• fundamental circle