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

Zenit (camera)

Zenit is a Russian camera brand manufactured by KMZ in the town of Krasnogorsk near Moscow since 1952 and by BelOMO in Belarus since the 1970s. The Zenit trademark is associated with 35mm SLR cameras...

.

Zenith cameras are astronomic or geodetic instruments which are directed exactly to 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...

. The star

Star

A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...

s are recorded either by photographic plates or by CCD

Charge-coupled device

A charge-coupled device is a device for the movement of electrical charge, usually from within the device to an area where the charge can be manipulated, for example conversion into a digital value. This is achieved by "shifting" the signals between stages within the device one at a time...

 sensors.

The main tasks in using these instruments are:

• Astrometry
  Astrometry
  Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of our Solar System and our Galaxy, the Milky...
  
   (determination of star positions
  Apparent places
  The wrong place of an object is the position in space as seen by the observer. Because of physical and/or geometrical effects it has a deviation from the "true position"....
  
   or of their proper motion
  Proper motion
  The proper motion of a star is its angular change in position over time as seen from the center of mass of the solar system. It is measured in seconds of arc per year, arcsec/yr, where 3600 arcseconds equal one degree. This contrasts with radial velocity, which is the time rate of change in...
  
  s)
• Geodetic
  Geodesy
  Geodesy , also named geodetics, a branch of earth sciences, is the scientific discipline that deals with the measurement and representation of the Earth, including its gravitational field, in a three-dimensional time-varying space. Geodesists also study geodynamical phenomena such as crustal...
  
   observation of the deflection
  Vertical deflection
  The vertical deflection at a point on the earth is a measure of how far the direction of the local gravity field has been shifted by local anomalies such as nearby mountains....
  
  s of the vertical direction
  Vertical direction
  In astronomy, geography, geometry and related sciences and contexts, a direction passing by a given point is said to be vertical if it is locally aligned with the gradient of the gravity field, i.e., with the direction of the gravitational force at that point...
  
  
• Contribution to the monitoring of the Earth rotation
  Earth rotation
  Earth's rotation is the rotation of the solid Earth around its own axis. The Earth rotates towards the east. As viewed from the North Star Polaris, the Earth turns counter-clockwise.- Rotation period :...
  
   and of the astronomical time system.

The small differences between the instrumental axis and the vertical is controlled by spirit level

Spirit level

A spirit level or bubble level is an instrument designed to indicate whether a surface ishorizontal or vertical . Different types of spirit levels may be used by carpenters, stonemasons, bricklayers, other building trades workers, surveyors, millwrights and other metalworkers, and in some...

s or by vertical sensor

Sensor

A sensor is a device that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument. For example, a mercury-in-glass thermometer converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated...

s.

Whereas the focal length

Focal length

The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus...

s of the astronomical

Astronomy

Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

 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

Geodetic astronomy

Geodetic astronomy is the application of astronomical methods into networks and technical projects of geodesy.The most important topics are:* Establishment of geodetic datum systems Geodetic astronomy is the application of astronomical methods into networks and technical projects of geodesy.The...

, Position astronomy, Geoid

Geoid

The geoid is that equipotential surface which would coincide exactly with the mean ocean surface of the Earth, if the oceans were in equilibrium, at rest , and extended through the continents . According to C.F...

, IERS

IERS

IERS may refer to:* International Earth Rotation and Reference Systems Service* Independent Electricity Retail Solutions Pty Ltd* Information Exchange Requirements - used within MODAF and DODAF as the OV-3 view - called Information Exchange Matrix....

, time service