Zenith camera

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For the Russian camera brand sometimes referred to as "Zenith", see Zenit (camera).

Zenith cameras are astronomic or geodetic instruments which are directed exactly to the zenith. The stars are recorded either by photographic plates or by CCD sensors.

The main tasks in using these instruments are:

• Astrometry (determination of star positions or of their proper motions)
• Geodetic observation of the deflections of the vertical direction
• Contribution to the monitoring of the Earth rotation and of the astronomical time system.

The small differences between the instrumental axis and the vertical is controlled by spirit levels or by vertical sensors.

Whereas the focal lengths of the astronomical instruments range from about 1 to 3 meters,
the geodetic zenith cameras are much more smaller (f ≈ 0.2 to 0.5 m). Some special instruments were developed in the 1990s by the Technical University of Hannover (northern Germany) and of the TU Wien (Austria).

See also: Geodetic astronomy, Position astronomy, Geoid, IERS, time service