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Star transits (Reticle 2°, magnif. ~10, two stars passing the vertical thread). Timing accuracy may be ±0,5 s.
A star transit is the passage of a star across the
field of view of a
telescope
eyepiece.
The precise observation of star transits is the basis of many methods in
astronomy and in
geodesy. The measurements can be done in different ways:
-
visually (mostly up to 1990): accuracy 0,1" to 2" (depending on the instrument); timing with digital clocks about 0,05–0,2 seconds
- by
CCD and other
electro-optical sensors: as above, time often better
- semi automatic instruments:
Photography or "
impersonal micrometer", ca. 2 times better than No.1
- by Scanning methods:
Astrometry
satellites like
Hipparcos about 0,01".
See also
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.