Telescope, Horizontal

a telescope whose optical axis is stationary and fixed on the plane of the horizon (usually in a north-south direction).

The horizontal telescope is used primarily for observing the sun and moon and, less often, the planets and stars. In a horizontal telescope a system of plane mirrors, including a mobile mirror moved by a clockwork mechanism (usually electric) reflects the light of a moving heavenly body constantly along the optical axis of the stationary telescope. The objective of a horizontal telescope, which can be a mirror (concave parabolic and, with a small aperture ratio, spherical) as well as a lens, projects the image of a heavenly body on a photoreceptive instrument, such as a spectrograph, a spec-trohelioscope, a spectroheliograph, or a magnetograph.