circle of equal altitude

circle of equal altitude

[′sər·kəl əv ′ē·kwəl ′al·tə‚tüd]
(geodesy)
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.

circle of equal altitude

circle of equal altitudeclick for a larger image
A circle on the surface of the earth, having as its center the substellar points of a given celestial body, from any point on or above the circumference of which the angular altitude of the body is the same. Also called a circle of position.
References in periodicals archive ?
To remain at fixed altitude with respect to Star B, the observer is always located on a circle of equal altitude whose center on earth is the Geographical Position, directly below Star B at its zenith.
A ship's course would not follow the periphery of a single circle of equal altitude as modern calculations do; rather, it would follow the route dictated by the destinations of its cargo.
So long as the ship sailed within a latitude range whose width never exceeded the diameter selected for the circle of equal altitude of the fettered star, as shown in figure 4, the navigator could use the al-qaid method.
This results from measuring altitudes in the alqaid case from star to periphery of the circle of equal altitude which continuously bends away from or toward the unfettered star, thus giving greater incremental extensions of horizontal distance per 1 |degree~ of latitude change compared to the abdal case, where measurements are made from star to meridian.
The fettered altitude, 10 |degrees~, is low, so the diameter of the circle of equal altitude is very large.
For each successive position of observer, it is necessary to determine a new longitude position of the observer as he moves 1 |degree~ latitude on the circle of equal altitude.
10 Al-qaid, the second method employed by medieval Arab navigators in determining latitude, quite ingeniously anticipates the modern circle of equal altitude used in conjunction with the navigational triangle to duplicate the medieval empirical process.
11 To visualize a circle of equal altitude, picture a maypole with children encircling the pole, each holding a streamer attached to the top of the pole.