World Library  
Flag as Inappropriate
Email this Article

Spherical astronomy

Article Id: WHEBN0002039039
Reproduction Date:

Title: Spherical astronomy  
Author: World Heritage Encyclopedia
Language: English
Subject: Celestial sphere, Parallactic angle, Spherical astronomy, Astrological aspects, Analog computer
Collection: Astrological Aspects, Astrometry, Spherical Astronomy
Publisher: World Heritage Encyclopedia

Spherical astronomy

Spherical astronomy or positional 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. It relies on the mathematical methods of spherical geometry and the measurements of astrometry.

This is the oldest branch of astronomy and dates back to antiquity. Observations of celestial objects have been, and continue to be, important for religious and astrological purposes, as well as for timekeeping and navigation. The science of actually measuring positions of celestial objects in the sky is known as astrometry.

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 is 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 effects 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 (a table of values that gives the positions of astronomical objects in the sky at a given time) is used, which can then be converted into suitable real-world coordinates.

The unaided human eye can detect about 6000 stars, of which about half are below the horizon at any one time. On modern star charts, the celestial sphere is divided into 88 constellations. Every star lies within a constellation. Constellations are useful for navigation. Polaris lies close to due north to an observer in the northern hemisphere. This star is always at a position nearly over the North Pole.


  • Positional phenomena 1
  • Ancient structures associated with positional astronomy include 2
  • External links 3
    • Software 3.1
  • References 4
  • See also 5

Positional phenomena

Ancient structures associated with positional astronomy include

External links

Course Notes and Tutorials

  • Professor Vincent's course notes at the University of St.Andrews
  • From Stephen Tonkin's Astronomy tutorials
  • From Professor Kirkman's tutorials at College of Saint Benedict + Saint John's University


NOVAS, an integrated package of subroutines for the computation of a wide variety of common astrometric quantities and transformations, in Fortran and C, from the U.S. Naval Observatory.

jNOVAS, is a java wrapper for library developed and distributed by The United States Naval Meteorology and Oceanography Command (NMOC) with included JPL planetary and lunar ephemeris DE421 binary file published by the Jet Propulsion Laboratory.


  • Robin M. Green, Spherical Astronomy, 1985, Cambridge University Press, ISBN 0-521-31779-7
  • 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)

See also

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.