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The vertical circle is an
The vertical circle is an optical instrument
An optical instrument is a device that processes light waves (or photons), either to enhance an image for viewing or to analyze and determine their characteristic properties. Common examples include periscopes, microscopes, telescopes, and camera ...
used to measure angles in astronomy
Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest includ ...
, which name is derived from the mathematical concept of the vertical circle
In spherical geometry, a vertical circle is a great circle on the celestial sphere that is perpendicular to the horizon. Therefore, it contains the vertical direction, passing through the zenith and the nadir. There is a vertical circle for any g ...
from spherical geometry
300px, A sphere with a spherical triangle on it.
Spherical geometry or spherics () is the geometry of the two-dimensional surface of a sphere or the -dimensional surface of higher dimensional spheres.
Long studied for its practical applicati ...
. It is a device for measuring astronomical angles, which can be rotated in altitude and azimuth. It consists of a telescope
A telescope is a device used to observe distant objects by their emission, Absorption (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally, it was an optical instrument using len ...
(in astronomical geodesy
Geodetic astronomy or astronomical geodesy (astro-geodesy) is the application of astronomical methods into geodetic networks and other technical projects of geodesy.
Applications
The most important applications are:
* Establishment of geode ...
occasionally also with a reflecting telescope
A reflecting telescope (also called a reflector) is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century by Isaac Newton as an alternati ...
), which is mounted on a horizontal tilting axis and is supported by a stable 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 ...
. It is similar in design to the meridian circle
The meridian circle is an instrument for timing of the passage of stars across the local meridian, an event known as a culmination, while at the same time measuring their angular distance from the nadir. These are special purpose telescopes moun ...
, but the latter only has a horizontal tilting axis without the means to change azimuth. The angular movements around the tilting and standing axes are measured with large, finely divided circles and a reading microscope
A microscope () is a laboratory equipment, laboratory instrument used to examine objects that are too small to be seen by the naked eye. Microscopy is the science of investigating small objects and structures using a microscope. Microscopic ...
.{{cite book , last=Chauvenet , first=William , author-link=William Chauvenet , date=1863 , title=A Manual of Spherical and Practical Astronomy , volume=II: Theory and use of astronomical instruments , url=https://books.google.com/books?id=AVI8pz41ia8C&pg=PA315 , location=Philadelphia , publisher=J.B. Lippincott & Co. , page=315 , quote=Chapter VII. The Altitude and Azimuth Instrument. .Sometimes the horizontal circle is reduced to small and designed simply as a finder or to set the instrument approximately at a given azimuth while the vertical is made of unusually large dimensions and is intended for most refined astronomical measurement. The instrument is then known simply as a ''vertical circle''. Such is the ERTEL Vertical Circle of the Pulkova Observatory, the telescope of which has a focal length of 77 inches, and its vertical circle a diameter of 43 inches.
Instruments like this were more common in 19th century observatories and were important for locating and recording coordinates in the cosmos, and observatories often had various other instruments for certain functions as well as advanced clocks of the period. The popularly known example in the observatories, was the Great Refractors which became larger and larger and came to have a dominating effect to the point that observatories were moved simply to have better conditions for their biggest telescope, in the modern style where observatories often have one instrument only in a remote location on the Earth or even in outer space. However, in the 19th century it was more basic with observatories often making recording of coordinates of different items and to determine the shape of the Earth and times.
See also
*Meridian circle
The meridian circle is an instrument for timing of the passage of stars across the local meridian, an event known as a culmination, while at the same time measuring their angular distance from the nadir. These are special purpose telescopes moun ...
*Equatorial telescope
An equatorial mount is a mount for instruments that compensates for Earth's rotation by having one rotational axis, called ''polar axis'', parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cam ...
* Comet seeker
References