Recording micrometer

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The recording micrometer or impersonal micrometer is an additional device for increasing the accuracy of astronomical and astro-geodetic measurements. It enables the unavoidable reaction time when measuring star passages - the so-called personal equation  - and the passage error to be significantly reduced. It was invented by Carl Braun in 1867 . In 1889 it was redesigned in a simpler form by the German instrument manufacturer Johann Adolf Repsold .

Construction

The micrometer is built into the eyepiece of larger measuring instruments ( DKM3-A , Wild T4 ), in which the thread network contains not only the fixed lines but also a movable thread . If the observer continuously follows the star with it , electrical contacts are closed at precisely defined angular intervals , which trigger a time registration .

Instead of observing a star passage on many individual "threads" of a network of threads , the impersonal micrometer allows a "moving thread" to continuously track the star. Meanwhile, the micrometer (connected to a measuring spindle) closes electrical contacts at defined points every few seconds , so that the passage of the star can be registered with the same accuracy as the observer follows the star with.

The main advantage of the instrument is the reduced impact of response time , which in astronomy is called "personal equation". While it is between 0.1 and 0.3 seconds for different people with timekeeping with the hand and digital stopwatch and varies by about 0.04 seconds depending on the current state of mind, the recording micrometer lowers both values ​​by about half.

See also

Technical literature and web link

  • K. Ramsayer , 1969: Geodetic Astronomy , Volume IIa of the Handbook of Surveying, JB Metzler-Verlag Stuttgart.
  • G. Gerstbach , 1975: Analysis of personal errors in passage observations of stars. Geoscientific Communications, Volume 7, pp. 51–102, TU Wien.
  • A. Schödlbauer, 2000: Geodetic Astronomy - Basics and Concepts. , De Gruyter-Verlag Berlin / New York.

Individual evidence

  1. ^ Paul Labitzke:  Braun, Carl. In: New German Biography (NDB). Volume 2, Duncker & Humblot, Berlin 1955, ISBN 3-428-00183-4 , p. 553 f. ( Digitized version ).