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A zenith telescope is a type of
Zenith Sector by John Bird
{{Portal bar, Astronomy, Stars, Spaceflight, Outer space, Solar System Telescope types
A zenith telescope is a type of telescope
A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to obse ...
that is designed to point straight up at or near the zenith
The zenith (, ) is an imaginary point directly "above" a particular location, on the celestial sphere. "Above" means in the vertical direction ( plumb line) opposite to the gravity direction at that location ( nadir). The zenith is the "high ...
. They are used for precision measurement of star positions, to simplify telescope construction, or both.
A classic zenith telescope, also known as a zenith sector employs a strong altazimuth mount
An altazimuth mount or alt-azimuth mount is a simple two- axis mount for supporting and rotating an instrument about two perpendicular axes – one vertical and the other horizontal. Rotation about the vertical axis varies the azimuth (compass b ...
, fitted with levelling screws. Extremely sensitive levels are attached and the telescope has an eyepiece fitted with a micrometer Micrometer can mean:
* Micrometer (device), used for accurate measurements by means of a calibrated screw
* American spelling of micrometre
The micrometre ( international spelling as used by the International Bureau of Weights and Measures; ...
. They are used for the measurement of small differences of zenith
The zenith (, ) is an imaginary point directly "above" a particular location, on the celestial sphere. "Above" means in the vertical direction ( plumb line) opposite to the gravity direction at that location ( nadir). The zenith is the "high ...
distance, and used in the determination of astronomic latitude
In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north po ...
.
Other types of zenith telescopes include the Monument to the Great Fire of London, which includes a central shaft meant for use as a zenith telescope. High-precision (and fixed building) zenith telescopes were also used until the early 1980s to track Earth's north pole position e.g. Earth's rotation axis position ( polar motion). Since then radio astronomical quasar
A quasar is an extremely luminous active galactic nucleus (AGN). It is pronounced , and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from a galaxy nucleus is powered by a supermassive black hole with a mass rangin ...
measurements ( VLBI) have also measured Earth's rotation axis several orders of magnitude more accurately than optical tracking.
The NASA Orbital Debris Observatory, which used a 3 m diameter aperture liquid mirror, and the Large Zenith Telescope, which uses a 6 m diameter aperture liquid mirror, are both zenith telescopes, as the use of liquid mirror meant that these telescopes could only point straight up.
See also
* List of astronomical instruments *List of telescope types
The following are lists of devices categorized as types of telescopes or devices associated with telescopes. They are broken into major classifications with many variations due to professional, amateur, and commercial sub-types. Telescopes can be ...
* Zenith camera
References
External links
Zenith Sector by John Bird
{{Portal bar, Astronomy, Stars, Spaceflight, Outer space, Solar System Telescope types