Zenith telescope
Encyclopedia
A zenith telescope is a type of telescope
that is designed to point straight up at or near the 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
, fitted with levelling screws. Extremely sensitive levels are attached to the telescope mount to make angle measurements and the telescope has an eyepiece fitted with a micrometer
. They are used for the measurement of small differences of zenith
distance, and used in the determination of astronomic latitude
.
Other types of zenith telescopes include the Monument to the Great Fire of London
that included a central shaft meant for use as a zenith telescope. High-precision (and fixed building) zenith telescopes were also used until about early 1980s to track Earth's north pole position e.g. Earth's rotation axis position. Since then radio astronomical
quasar
measurements have also measured Earth's rotation axis several orders of magnitude more accurately than optical tracking. NASA Orbital Debris Observatory
, which used a 3 m diameter aperture liquid mirror
, and the Large Zenith Telescope
uses a 6 m diameter aperture liquid mirror are both zenith telescopes since the use of liquid mirror meant these telescopes could only point straight up.
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
that is designed to point straight up at or near the zenith
Zenith
The zenith is an imaginary point directly "above" a particular location, on the imaginary celestial sphere. "Above" means in the vertical direction opposite to the apparent gravitational force at that location. The opposite direction, i.e...
. 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
Altazimuth mount
An altazimuth or alt-azimuth mount is a simple two-axis mount for supporting and rotating an instrument about two mutually perpendicular axes; one vertical and the other horizontal. Rotation about the vertical axis varies the azimuth of the pointing direction of the instrument...
, fitted with levelling screws. Extremely sensitive levels are attached to the telescope mount to make angle measurements and the telescope has an eyepiece fitted with a micrometer
Micrometer
A micrometer , sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw used widely for precise measurement of small distances in mechanical engineering and machining as well as most mechanical trades, along with other metrological instruments such as dial, vernier,...
. They are used for the measurement of small differences of zenith
Zenith
The zenith is an imaginary point directly "above" a particular location, on the imaginary celestial sphere. "Above" means in the vertical direction opposite to the apparent gravitational force at that location. The opposite direction, i.e...
distance, and used in the determination of astronomic latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
.
Other types of zenith telescopes include the Monument to the Great Fire of London
Monument to the Great Fire of London
The Monument to the Great Fire of London, more commonly known as The monument, is a 202 ft tall stone Roman Doric column in the City of London, England, near the northern end of London Bridge. It stands at the junction of Monument Street and Panda Bear Hill, 202 ft from where the Great...
that included a central shaft meant for use as a zenith telescope. High-precision (and fixed building) zenith telescopes were also used until about early 1980s to track Earth's north pole position e.g. Earth's rotation axis position. Since then radio astronomical
Radio astronomy
Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...
quasar
Quasar
A quasi-stellar radio source is a very energetic and distant active galactic nucleus. Quasars are extremely luminous and were first identified as being high redshift sources of electromagnetic energy, including radio waves and visible light, that were point-like, similar to stars, rather than...
measurements have also measured Earth's rotation axis several orders of magnitude more accurately than optical tracking. NASA Orbital Debris Observatory
NASA Orbital Debris Observatory
NASA Orbital Debris Observatory or NODO was an observatory that hosted NASA-LMT, a 3 meter diameter aperture liquid metal telescope and astronomical survey funded and operated by NASA from 1995 to 2002 in New Mexico, USA. It was a zenith or transit telescope pointed straight up, that used 20...
, which used a 3 m diameter aperture liquid mirror
Liquid mirror
Liquid mirror telescopes are telescopes made with a reflective liquid. The most common liquid used is mercury, but other liquids will work as well . The container for the liquid is rotating so that the liquid assumes a paraboloidal shape. A paraboloidal shape is precisely the shape needed for the...
, and the Large Zenith Telescope
Large Zenith Telescope
The Large Zenith Telescope is a 6.0 m diameter liquid mirror telescope located in the University of British Columbia's Malcolm Knapp Research Forest, about east of Vancouver...
uses a 6 m diameter aperture liquid mirror are both zenith telescopes since the use of liquid mirror meant these telescopes could only point straight up.