The precise observation of star transits is the basis of many methods in Astronomy and in Geodesy. The measurements can be done in different way:

1. visually (mostly up to 1990): accuracy 0,1" to 2" (depending on the instrument); timing with digital clocks about 0,05-0,2 seconds
2. by CCD- and other elektro optical sensors: as above, time often better
3. semi automatic instruments: Photography or "impersonal micrometer", ca. 2 times better than No.1
4. by Scanning methods: Astrometry satellites like Hipparcos about 0,01".

See also

• Meridian circle
• Passage instrument
• Theodolite
• angular measurement
• accuracy
• precision
• Instrument errors
• Arc seconds
• angular mil

Literature

• Karl Ramsayer, 1969: Geodätische Astronomie, Vol.2a of Handbuch der Vermessungskunde, 900 p., J.B.Metzler-Verlag Stuttgart.
• Ivan I. Mueller, 1969: Spherical and Practical Astronomy as applied to Geodesy, 610 p., Fred.Ungar publ., USA
• IAU Coll.48: Modern Astrometry, Egermann, University Vienna.