The Astrometrie ( gr. Ἄστρον = star and μέτρον, métron = dimension, measuring) is the geometric portion of astronomy and as such, the counterpart of astrophysics . It is also called positional astronomy or classical astronomy and includes the measurement and calculation of star positions (so-called star locations ) and their movements in precisely defined reference systems . This makes it the basis of much astronomical research and especially celestial mechanics . Until the establishment of astrophysics, which began around 1860 after the invention of spectroscopy, astrometry and spherical astronomy made up the majority of all astronomy.
According to de Vegt , astrometry is the science of the geometric structure of the universe (location, movement and distance of the stars) or the measurement of the sky . At the same time, it provides a coordinate basis for geodesy - i.e. the measurement of the earth .
Tasks of astrometry
More specifically, astrometry means today:
- Creation of catalogs with precise positions and movements of stars
- Construction of the fundamental reference coordinate system of astronomy and geosciences
- Development of spatial astronomical databases
- Development of measurement methods and instruments
- Implementation of the relevant measurements and international measurement campaigns
- Reduction of measurements and standardization of the corresponding procedures.
The most important institution for these aspects is the Astronomical Computing Institute (ARI) in Heidelberg . It operates astrometry, stellar dynamics and astronomical services in the form of ephemeris and yearbooks , calendar bases and bibliographies .
Historical and cross connections
Until the advent of astrophysics after 1850 - mainly through spectral analysis and astrophotography - (according to Karl Schütte ) astrometry was synonymous with astronomy in general. It was not until the 20th century that people began to speak of astrometry or positional astronomy - in contrast to astrophysics , which dominated astronomy from 1950 onwards.
Between 1960 and 1990 astrometry almost led a niche existence, as barely 10% of astronomers (but increasingly geodesics ) devoted themselves to it . But when the era of astrometry satellites and CCD sensors began, this changed and today the high-precision measurement methods of astrometry also bring significant impulses and the like. a. for celestial mechanics , space travel, cosmology and stellar dynamics or Milky Way research .
The pioneers of "classic" astrometry are above all
- Hipparchus , on the first star catalog with over 1000 stars back and the slow coordinates offset by the precession discovered
- Ptolemy , who summarized the astronomical theories of his time in the Almagest
- Tycho Brahe , who - still without a telescope - achieved measuring accuracies of up to 0.01 °
- the astronomers of Europe participating in the Sky Police, who created the first precise star catalogs around 1800 (e.g. Giuseppe Piazzi )
- Friedrich Wilhelm Bessel , who succeeded in the first measurement of a fixed star distance
- Friedrich Argelander and his 325,000 star Bonn survey , which the German Astronomical Society further developed into the system of AGK catalogs
- Simon Newcomb , whose definition of the fundamental system lasted almost 100 years
- the Heidelberg Astronomical Computing Institute and the US Naval Observatory
- the project groups of the astrometric satellites Hipparcos and Gaia
Astrometry has experienced a renaissance since the development of optoelectronic sensors and Very Long Baseline Interferometry . Their links to geodesy are becoming stronger, and the importance of high-precision coordinate systems is increasing. International tasks such as monitoring the earth's rotation with radio astronomy and GPS , space travel and satellite projects such as Galileo or GAIA are becoming interdisciplinary and give young astronomers new career opportunities. In defining the time systems , astronomers have to cooperate with physics and another three to four disciplines.
Two to four dimensional astrometry
The 2-D -part astrometry belongs to spherical astronomy and deals only with the incidence direction of light sources from the space - in theory, measuring techniques, as to the coordinate systems and for various reductions in the apparent direction of celestial objects ( planets , stars , galaxies ) to their true direction .
The star locations become three-dimensional by measuring parallaxes - those apparent annual shifts that can be determined from opposite points on the earth's orbit . From this, star distances of up to 100 light years can be derived, and with Hipparcos and other methods, far more.
Finally, 4-D could be called stellar dynamics , which is based on proper movements . They are obtained from precise asterisk words from widely spaced epochs . Its addition to the spatial velocity vector gives the radial velocity , a result of the spectral analysis and thus the transition to astrophysics . The situation is similar when determining distances using photometry .
Use for astronomical research
Precise star coordinates , distance and speed data fertilize many aspects of astronomy. Some of them are:
- Better spatial picture of the star distribution and the movement conditions
- Dynamics of the Milky Way in our environment
- More precise determination of the star distribution in terms of the combination of luminosity and spectral type in the Hertzsprung-Russell diagram
- More precise basis for measuring the earth and the solar system
- More precise prediction of star coverages by planets and minor planets ( asteroids ).
- Basis for high-precision astrometry up to the most distant galaxies
- Connection of the optical coordinate frame to that of radio interferometry with quasars ; see VLBI , Geodesy .
- Julius Redlich: A look into the most general network of terms in astrometry . Beyer publishing house, Langensalza 1907.
- Rudolf Sigl : Geodetic Astronomy . 3. Edition. Verlag Wichmann, Heidelberg 1991, ISBN 3-87907-190-X .
- Albert Schödlbauer : Geodetic Astronomy - Basics and Concepts . De Gruyter, Berlin / New York 2000, ISBN 3-11-015148-0 .
- P. Brosche, Harald Schuh : New developments in astrometry and their significance for geodesy . In: Journal of Surveying (ZfV) . 1999, ISSN 0044-3689 , p. 343-350 (vol. 124).
- Jean Kovalevsky, (et al.): Fundamentals of astrometry . Cambridge Univ. Press, Cambridge 2004, ISBN 0-521-64216-7 .
- Jean Kovalevsky: Modern astrometry . Springer, Berlin 2002, ISBN 3-540-42380-X .
- Stephen Webb: Measuring the universe - the cosmological distance ladder . Springer, London 2001, ISBN 1-85233-106-2 .
- Michael Perryman: Astronomical Applications of Astrometry: Ten Years of Exploitation of the Hipparcos Satellite Data . Cambridge Univ. Press, Cambridge 2008, ISBN 978-0-521-51489-7 .
- Astrometry UNI Heidelberg
- University of Hamburg
- Information about astrometry
- Official website of the International VLBI Service for Geodesy and Astrometry (IVS) (in English)