# Zenith telescope

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Type of telescope that points straight up

This modern liquid-mirror telescope aims upward

A **zenith telescope** is a type of [telescope](/source/Telescope) that is designed to point straight up at or near the [zenith](/source/Zenith). 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](/source/Altazimuth_mount), fitted with levelling screws. Extremely sensitive levels are attached and the telescope has an eyepiece fitted with a [micrometer](/source/Micrometer_(device)).[1] They are used for the measurement of small differences of [zenith](/source/Zenith) distance, and used in the determination of astronomic [latitude](/source/Latitude).

Other types of zenith telescopes include the [Monument to the Great Fire of London](/source/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](/source/Earth's_rotation) axis position ([polar motion](/source/Polar_motion)). Since then [radio astronomical](/source/Radio_astronomy) [quasar](/source/Quasar) measurements ([VLBI](/source/VLBI)) have also measured Earth's rotation axis several orders of magnitude more accurately than optical tracking.

The [NASA Orbital Debris Observatory](/source/NASA_Orbital_Debris_Observatory) with an [aperture](/source/Aperture) of 3 m and the [Large Zenith Telescope](/source/Large_Zenith_Telescope) with an aperture of 6 m are constructed as zenith telescopes, as the use of [liquid mirrors](/source/Liquid-mirror_telescope) limits them to pointing straight up.[2]

Zenith Telescope Astronomical transit and zenith telescope, 1898 Ramsden's zenith telescope.

## See also

- [List of astronomical instruments](/source/List_of_astronomical_instruments)

- [List of telescope types](/source/List_of_telescope_types)

- [Zenith camera](/source/Zenith_camera)

## References

1. **[^](#cite_ref-1)** [Chisholm, Hugh](/source/Hugh_Chisholm), ed. (1911). ["Geodesy"](https://en.wikisource.org/wiki/1911_Encyclop%C3%A6dia_Britannica/Geodesy). *[Encyclopædia Britannica](/source/Encyclop%C3%A6dia_Britannica_Eleventh_Edition)*. Vol. 11 (11th ed.). Cambridge University Press. pp. 607–615.

1. **[^](#cite_ref-2)** Cabanac, Rémi A.; Borra, Ermanno F.; Beauchemin, Mario (1998). "A Search for Peculiar Objects with the NASA Orbital Debris Observatory 3 Meter Liquid Mirror Telescope". *The Astrophysical Journal*. **509** (1): 309. [arXiv](/source/ArXiv_(identifier)):[astro-ph/9804267](https://arxiv.org/abs/astro-ph/9804267). [Bibcode](/source/Bibcode_(identifier)):[1998ApJ...509..309C](https://ui.adsabs.harvard.edu/abs/1998ApJ...509..309C). [doi](/source/Doi_(identifier)):[10.1086/306488](https://doi.org/10.1086%2F306488). [S2CID](/source/S2CID_(identifier)) [119434586](https://api.semanticscholar.org/CorpusID:119434586).

## External links

- [Zenith Sector by John Bird](http://www.mhs.ox.ac.uk/students/96to97/zenith.htm)

[Portals](https://en.wikipedia.org/wiki/Wikipedia:Contents/Portals):
- [Astronomy](https://en.wikipedia.org/wiki/Portal:Astronomy)
- [Stars](https://en.wikipedia.org/wiki/Portal:Stars)
- [Spaceflight](https://en.wikipedia.org/wiki/Portal:Spaceflight)
- [Outer space](https://en.wikipedia.org/wiki/Portal:Outer_space)
- [Solar System](https://en.wikipedia.org/wiki/Portal:Solar_System)

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Adapted from the Wikipedia article [Zenith telescope](https://en.wikipedia.org/wiki/Zenith_telescope) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Zenith_telescope?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.