Kuffner-Sternwarte Wien Vertikalkreis 2015 04

astronomy Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...

, a vertical circle is a

great circle In mathematics, a great circle or orthodrome is the circular intersection of a sphere and a plane passing through the sphere's center point. Any arc of a great circle is a geodesic of the sphere, so that great circles in spherical geomet ...

on the

celestial sphere In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, ...

that is perpendicular to the

horizon The horizon is the apparent line that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This line divides all viewing directions based on whether i ...

. Therefore, it contains the

vertical direction In astronomy, geography, and related sciences and contexts, a '' direction'' or ''plane'' passing by a given point is said to be vertical if it contains the local gravity direction at that point. Conversely, a direction or plane is said to be hor ...

, passing through 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 "highest" ...

and the

nadir The nadir (, ; ar, نظير, naẓīr, counterpart) is the direction pointing directly ''below'' a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface. The direc ...

. There is a vertical circle for any given

azimuth An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematicall ...

, where azimuth is the angle measured east from the north on the celestial horizon. The vertical circle which is on the east–west direction is called the

prime vertical In astronomy, astrology, and geodesy, the prime vertical or first vertical is the vertical circle passing east and west through the zenith of a specific location, and intersecting the horizon in its east and west points. In other words, the prime ...

. The vertical circle which is on the north–south direction is called the local celestial meridian (LCM), or principal vertical. Vertical circles are part of the

horizontal coordinate system The horizontal coordinate system is a celestial coordinate system that uses the observer's local horizon as the fundamental plane to define two angles: altitude and azimuth. Therefore, the horizontal coordinate system is sometimes called as th ...

. 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, were the Great refractors which became larger and larger and came to have 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 observatorys often making recording of coordinates of different items and to determine the shape of the Earth and times.

References

Astronomical coordinate systems {{Astronomy-stub

See also

References