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Star transit

Passage of a star across the field of view of a telescope eyepiece

Wikipedia contributorsAdapted for Fathomly · View authors
1 min read
Source updated April 10, 2026
Image credit is listed at the end of this article.

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:

  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 electro-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".

01Literature

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This article is adapted from the Wikipedia article “Star transit”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.

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Related topics

Accuracy and precision

Accuracy and precision are measures of observational error; accuracy is how close a given set of measurements is to the true value and precision is how close the measurements are to each other. The International Organization for Standardization defines a related measure: trueness, "the closeness of agreement between the arithmetic mean of a large number of test results and the true or accepted reference value." While precision is a description of random errors (a measure of statistical variability), accuracy has two different definitions: More commonly, a description of systematic errors (a measure of statistical bias of a given measure of central tendency, such as the mean).

Instrument error

Instrument error refers to a measurement error inherited from a measuring instrument. It could be caused by manufacturing tolerances of components in the instrument, the accuracy of the instrument calibration, or a difference between the measurement condition and the calibration condition.

Meridian circle

The meridian circle is an instrument for timing of the passage of stars across the local meridian, an event known as a culmination, while at the same time measuring their angular distance from the nadir. These are special purpose telescopes mounted so as to allow pointing only in the meridian, the great circle through the north point of the horizon, the north celestial pole, the zenith, the south point of the horizon, the south celestial pole, and the nadir.