Transit instrument

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In astronomy, transit instruments are used for the precise observation of star positions. The instruments can be divided into three groups:

Meridian circle at the Kuffner-Observatory in Vienna, Austria

1 Meridian instruments
2 Universal instruments
3 Zenith instruments and Astrolabes
4 Observation techniques and accuracy
5 See also
6 External links

[edit] Meridian instruments

for observation of star transits in the exact direction of South or North:

Meridian circles, Mural quadrants etc.
Passage instruments (transportable, also for prime vertical transits)

[edit] Universal instruments

which allow transit measurements in anyone direction

Astronomical theodolites
Altaz telescopes with graduated eyepieces (also for satellite transits)
Kine theodolites

[edit] Zenith instruments and Astrolabes

Zenith telescope
Photozenith tube (PZT)
zenith cameras
Danjon astrolabe, Zeiss Ni2 astrolabe, Circumzenital

[edit] Observation techniques and accuracy

Depending on the type of instrument, the measurements are carried out

visually and manual time registration (stopwatch, Auge-Ohr-Methode, chronograph)
visually by impersonal micrometer (moving thread with automatic registration)
photographic registration
CCD or other electro optic sensors.

The accuracy reaches from 0.2" (theodolites, small astrolabes) to 0.01" (modern meridian circles, Danjon). Early instruments (like the mural quadrants of Tycho Brahe) had no telescope and were limited to about 0.01°.