Transit instrument

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

File:Meridian Circle - Kuffner Observatory.jpg

Meridian circle at the Kuffner observatory in Vienna, Austria

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)

Universal instruments

which allow transit measurements in any direction

• Theodolite (Describing a theodolite as a transit may refer to the ability to turn the telescope a full rotation on the horizontal axis, which provides a convenient way to reverse the direction of view, or to sight the same object with the yoke in opposite directions, which causes some instrumental errors to cancel.) (Wolf and Brinker 183–6)
• Altaz telescopes with graduated eyepieces (also for satellite transits)
• Cinetheodolites

Zenith instruments and Astrolabes

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

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°.

See also

• Astronomical transit
• Position astronomy, Astrogeodesy
• latitude/longitude observation, vertical deflection

Works cited

Wolf, Paul R and Russell C. Brinker. Elementary Surveying, 8th ed. New York: Harper Collins, 1989.

External links

• Karl Ramsayer: Geodätische Astronomie, Vol.2a of Handbuch der Vermessungskunde, 900 p., J.B.Metzler, Stuttgart 1969
• Cauvenet and Brünnow's Handbooks of Spherical Geodesy
• Transit instrument in the Encyclopedia.com
• Transit circle technique (Classic Encyclopedia)
• Great Transit at Lick Observatory, +Photo
• Modern roboter telescopes
• The Carlsberg Automatic Meridian Circle
• Photo of a 19th century transit instrument (Jones 1826)
• Transit instruments udes by the Survey of India, 1867)