Spherical astronomy
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Spherical astronomy is the branch of astronomy that is used to determine the location of objects on the celestial sphere, as seen at a particular date, time, and location on the Earth. This is one of the oldest branches of astronomy. It relies on the mathematical methods of spherical geometry and the measurements of astrometry. This branch is also known as positional astronomy.
The primary elements of spherical astronomy are coordinate systems and time. The coordinates of objects on the sky are listed using the equatorial coordinate system, which are based on the projection of the Earth's equator onto the celestial sphere. The position of an object in this system is given in terms of right ascension (α) and declination (δ). The latitude and local time can then be used to derive the position of the object in the horizontal coordinate system, consisting of the altitude and azimuth.
The coordinates of celestial objects such as stars and galaxies are tabulated in a star catalog, which gives the position for a particular year. However the combined effects of precession and nutation will cause the coordinates to change slightly over time. The effect of these changes in the movement of the Earth are compensated by the periodic publication of revised catalogs.
To determine the position of the Sun and planets, an astronomical ephemeris is used. This gives the positions of these objects on the celestial sphere at a particular date and time, which can then be converted into suitable coordinates.
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Course Notes and Tutorials
[edit] References
- Robin M. Green, Spherical Astronomy, 1985, Cambridge University Press, ISBN 052137797.
- William M. Smart, edited by Robin M. Green, Textbook on Spherical Astronomy, 1977, Cambridge University Press, ISBN 0-521-29180-1. (This classic text has been re-issued).
[edit] See also
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