Horizon

The line of the blending of earth (or sea) and sky; the apparent meeting of the earth and heaven.

Apparent Horizon. (See Visible Horizon.)

Artificial Horizon. A reflector of quicksilver placed on the ground and used for observing altitudes of the heavenly bodies.

Celestial Horizon. The great circle in which the planes of the sensible and rational horizons produced cut the celestial sphere.

Dip of the Horizon. The angle between the visible and sensible horizons.

Rational Horizon. An imaginary great circle, the plane of which passes through the earth's centre, the poles being the zenith and nadir, and which divides the globe into two equal parts--parallel with the sensible horizon.

Sea Horizon. The circle which bounds the view of the observer--the apparent meeting of sea and sky.

Sensible Horizon. A plane touching the earth at the point where the observer is situated, and which meets the celestial sphere in a circle.

Shore Horizon. When the sea horizon is hidden by the intervention of land, the beach line is known as the shore horizon.

Visible Horizon. When the observer is elevated above the earth's surface by ordinary height of eye, or by standing on a vessel's deck, the limit of view is termed the visible or apparent horizon, and the angle between the visible and sensible horizons is called the dip of the horizon.