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Dictionary of Astrological and Astronomical Terms

Compiled by Julene Packer-Louis, Evan Bortnick, and Jackie Goldstein

Copyright 2000-2020 OCA, Inc. All rights reserved. No portion of the dictionary may be reproduced in any form without written permission.



An aspect refers to the angular relationships between planets, sensitive points or house cusps in the Horoscope. Lines drawn between any two points and the Earth (represented by the center of the chart) form the angle of the aspect. This is the equivalent to the number of degrees of arc between those two points.

The most common are the Ptolemeic or major aspects which are derived by dividing the 360 degrees of the circle by 0 (the Conjunction is 0 degrees between the two points), by 2 (the Opposition aspect is 180 degrees between the two points), by 3 (the Trine aspect which is 120 degrees between the two points), by 4 (the Square aspect which is 90 degrees between the two points) and by 6 ( the Sextile aspect which is 60 degrees between the two points).

The Ptolemaic aspects are based on Pythagorean numerology and the classical Greek theory of music, which identified certain harmonious ratios between the lengths of the strings of a musical instrument. The classical musical harmony ratios were 1:1, 1:2, 1:3, and 2:3. Only signs of the zodiac that formed classical musical ratios according to their spacing around the zodiac were considered to be in aspect. Thus, if an Opposition (totaling 6 signs) represents a straight line, then the ratio of a Square (3 signs) to an Opposition is 1:2, a Sextile (2 signs) to an Opposition is 2:6 or 1:3, a Trine (4 signs) to an Opposition is 4:6 or 2:3. The Semisextile (1 sign) and the Quincunx (5 signs) were not considered valid aspects because 1:6 and 5:6 were not regarded as ratios of musical harmony.

The Square and the Opposition aspects are considered to be hard or challenging, while the Sextile and Trine are soft or easy aspects, meaning that the planets tend to cooperate with each other or are more harmonious. The Conjunction is neutral, and depending upon which planets are involved may be challenging or harmonious. A variety of minor aspects are also used and are derived by dividing the circle into further smaller divisions.

Aspects are not usually exact and an orb of influence is used within which the aspect is considered to be active. Astrologers have a wide range of ideas about how large the orb should be, but it is generally assumed that the closer to exact that and aspect is, the more potent it becomes.


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