An asterism is a cluster of stars, usually but not necessarily located within a constellation. It may have some pictorial significance of its own, such as the belt and sword of Orion. In modern astronomy, the stars of an asterism have no gravitational relationship with one another. They may be long distances apart in space, yet from the earth's surface they appear to be neighbours. Some well-known star clusters of astrology, like the Pleiades and Hyades of the constellation Taurus, or Praesepe in the center of Cancer, actually do travel together in the heavens and are not technically asterisms to astronomers. Because astrology developed two thousand years before scientists understood the actual movements of stars, however, astrologers' use of the term asterism retains its historical roots as a visually identifiable group of closely positioned stars.
Asterisms were the basis for the ancient Egyptian calendar decans as well as the lunar mansions (Nakshatras) of Indian astrology. As astrologers themselves shifted in ancient times from gazing at constellations and asterisms to reading planets in signs off an ephemeris most of the asterisms lost their utility in horoscopic astrology. The decans became simple 10-degree segments of the 30-degree signs; and the lunar mansions, 27 units of 13 degrees, 20 minutes. Astrologers who use fixed stars today, however, may include some of the smaller asterisms in their work.
- Wikipedia: Asterism (Astronomy)
- Star Names — Their Lore and Meaning (Richard Hinckley Allen, originally 1899)
- Wikipedia: Urania's Mirror (Astronomical star card set from 1824)
- Geoffrey Cornelius: The Starlore Handbook: An Essential Guide to the Night Sky. 176 pages. Chronicle Books, 1997 ISBN 0811816044 (ISBN13: 9780811816045)
- Weaving together astronomy, myth, and symbolism
Notes and References
- The plate shows the Hyades asterism in the face of the constellation, and the Pleiades in its shoulder
- Dated circa 1600 BC. The cluster of dots in the upper right portion of the disk is believed to be the Pleiades