Eichfeld (astronomy)
In astronomy , calibration fields are certain star fields in which the physical or statistical properties of the fixed stars contained therein are examined and compared with one another.
William Herschel first used the calibration field method at the end of the 18th century to explore the structure of the Milky Way . He selected 3400 star fields evenly distributed across the sky and counted the stars visible in his telescope. Under the simplistic assumption that they all have the same luminosity , he calculated from this how far the star system of the Milky Way could extend in the respective direction, and essentially obtained its lens shape . Herschel called his method oaks of heaven or the Star oak and is considered the founder of the stellar statistics .
The calibration field best known for amateur astronomy is the north polar sequence, or pole sequence for short . It is a selection of stars in the vicinity of the north celestial pole with precisely measured brightnesses . It has been divided into three fields of increasing star numbers and decreasing brightness. Overall, it contains visually and photographically determined stars from the second to the 17th magnitude and has long served as the primary standard system for photometry .
As a very precise complement to this, there are several hundred standard stars distributed over the whole sky with very precise brightnesses in several color ranges.
For the purposes of galactic stellar statistics there are the Selected Areas :
- 206 star fields of 1.25 x 1.25 ° distributed regularly and symmetrically to the galactic equator
- and an additional 46 in special areas of the Milky Way.
They are considered representative samples for the entire sky.
literature
- H. Zimmermann, A. Weigert: Lexicon of Astronomy. Spektrum-Verlag, Heidelberg-Berlin 1999
- Günter D. Roth: Kosmos Astronomiegeschichte , chapter "A picture of the Milky Way". Kosmos-Verlag, Stuttgart 1987
- Dieter Herrmann: The Milky Way. Stars, nebulae, star systems , p. 108ff. Kosmos Astrobibliothek, Stuttgart 2003
- Diedrich Wattenberg: Wilhelm Herschels star calibrations and views of the construction of the star system . In Die Naturwissenschaften , Heft 34/6, p. 161ff, Springer-Verlag 1947