Through error

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In astronomy and geodesy, the inevitable small measurement error that occurs when observing a star passage in the field of view of a telescope is referred to as passage error .

To this day, such measurements are mainly used in astrogeodesy , for example in the determination of geoid (measurement of vertical deviations ) or the precise orientation of special surveying networks . In contrast, in astronomy, visual measurements are seldom made; The sources of error on the passage instrument are about half as large as on the much smaller geodetic devices.

When measured visually, the passage error is on the order of one to a few arc seconds ; its proportions depend on the following influences:

  1. on the quality and magnification of the telescope
  2. the measurement method and the type of time recording
  3. on the experience and the momentary balance of the observer
  4. on the star's brightness and (to a lesser extent) the star's color
  5. the unrest in the air .

In the case of electronic measurement, the influence of (3), partly also of (2) and (4), does not apply. However, small systematic sources of error remain, which are summarized under instrumental errors .

Overall, the measurement error - recently also called measurement deviation - is made up of random and systematic components. The classic specialist literature also differentiates between the entry error (random error on the individual measuring thread ) and a target error (mainly dependent on the magnification).

Further analyzes (e.g. BK Ramsayer, G. Gerstbach) also show a passage error (in the narrower sense) that cannot be reduced below a certain amount per star passage even by averaging several measuring threads (or digital measuring devices).

The aiming error of a single measurement is geodetic measuring telescopes with about 30-fold magnification at about 1 " for experienced observers and 2-3" for inexperienced people. In addition, there is a time error which is around 0.1 to 0.3 seconds when using digital clocks . Depending on the speed of the star in the field of view, the two components add up to around 1-3 ", but can be reduced to less than 1" on average by measuring several threads.

literature

  • Albert Schödlbauer : Geodetic Astronomy - Basics and Concepts . De Gruyter-Verlag Berlin / New York 2000
  • Carl Theodor Albrecht : Formulas and auxiliary tables for geographic location determinations . 4th edition, 308 pages, Leipzig 1908
  • Gottfried Gerstbach : Analysis of personal errors in passage observations of stars . Scientific med. Volume 7, pp. 51-102, TU Wien 1975
  • Gottfried Gerstbach: The external accuracy of astronomical location determinations with the Ni2 astrolabe and the personal equation . General Surveying news volume 84, issue 11/12, Karlsruhe 1977
  • Karl Ramsayer : Geodetic Astronomy, Volume IIa of the Handbook of Surveying. 900 p., JBMetzler-Verlag, Stuttgart 1969
  • Karl Ramsayer: Automatic star tracking for astronomical theodolite . DGK series B, booklet 81, Munich 1962 (or K. Ruopp, series C / 100, 1966)
  • Wolfgang Torge : Geodesy , 2nd edition, Chapter 5.3 "Geodetic Astronomy". De Gruyter-Verlag Berlin / New York 2003
  • W. Uhink: Contact and timing errors in passage observations with the impersonal micrometer . P. 321 ff., Journal of Surveying 1949