Planetary orbit
As planetary orbits that are curves referred to the planet under the stars or in 3D through-space. Their movements are predominantly cyclical in character , i.e. they take place at regular time intervals.
Apparent planetary orbit
The apparent orbit is the track that the planet describes against the background of the fixed stars , i.e. on the starry sky . It runs in the form of periodic " planetary loops ", roughly annual between Jupiter and Neptune , which in the earlier geocentric view of the solar system were explained and represented by superimposed circles, the epicycles . Further irregularities caused by the elliptical orbits of the planets have been corrected by eccentrics and " center point equations ".
Such purely geometric calculations are also possible without knowledge of the physical causes. The initially puzzling phenomenon of the planetary loops was partly attributed to the influence of deities in ancient times and gave rise to the spread of astrology .
True planetary orbit
The real, spatial orbits of the planets are conditioned by the forces of gravity and run approximately in Kepler ellipses - i.e. in elliptical conic sections - around the sun ( see also: Kepler's laws ).
Due to the mutual attraction of the planets and their deviations from the spherical shape , orbital disturbances occur, which can change the orbital elements in the per mil range. They can be calculated using methods of celestial mechanics , but they generally elude a closed mathematical representation in all strictness (see also three-body problem ).
The "true" planetary orbits can therefore only be calculated as follows:
- in retrospect ( ex-post ),
- empirical (especially through numerical integration ) and
- with limited accuracy .
However, since the time of Johannes Kepler , this accuracy has been increased from a few parts per thousand to better than 1:10 million through developments in mathematics and measurement methods, a large part of which can be traced back to the impulses of space travel .
The conditions of the orbital times already led the ancient natural philosophers to assume that the "slow" planetary orbits run further out than the "rapid" orbits. Aristarchus first developed an idea of the true distances in the 3rd century BC. Chr.
literature
- Arnold Hanslmeier (2007): Introduction to Astronomy and Astrophysics , 2nd edition, Spektrum akademischer Verlag, ISBN = 978-3-8274-1846-3
- Karl Stumpff , HH Voigt (1972): Fischer Lexicon "Astronomy" , new edit. 7th edition, Fischer Taschenbuch Verlag
See also
Web links
- Are the planetary orbits stable? from the alpha-Centauri television series(approx. 15 minutes). First broadcast on Mar 26 2000.