Opposition (astronomy and astrology)

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Positional astronomy.svg

Opposition is a word used in astronomy and astrology to show when one celestial body is on the opposite side of the sky when viewed from a particular place (usually the Earth). In particular, two planets are in opposition to each other when their ecliptic longitudes differ by 180°. When the Moon is in opposition it is called full moon.[1]

The symbol of opposition is .

A planet (or asteroid or comet) is said to be "in opposition" when it is in opposition to the Sun as seen from the Earth. This is the best time to observe a planet because:

  • it is visible almost all night, rising around sunset, culminating around midnight and setting around sunrise;
  • its orbit brings it closest to the Earth, making it appear bigger and brighter.
  • the opposition effect increases the reflected light from bodies with unobscured rough surfaces

References[change | change source]

  1. U.S. Naval Observatory Nautical Almanac Office, P. Kenneth Seidelmann (ed) 1992. Explanatory supplement to the Astronomical Almanac. University Science Books, Mill Valley CA, 733. ISBN 0-935702-68-7