Chart basics · Signs · Beginner
Constellations and signs
Also called sign versus constellation
A zodiac sign is an equal 30° slice of the ecliptic; a constellation is an unequal region of sky with an official IAU boundary.
The twelve signs borrowed their names from constellations about two thousand years ago, when the two roughly lined up. They no longer do: precession has moved the signs about a whole sign's width against the stars, and the constellations along the ecliptic were never equal in size. The IAU's boundaries also put a thirteenth constellation, Ophiuchus, across the Sun's path. None of this changes the tropical zodiac, which is defined by the equinox, not by the stars.
Sources
- International Astronomical Union: Constellations (FAQ) (opens in a new tab) academic
- NASA (2016): Constellations and the Calendar (opens in a new tab) technical
Written for Cool Moon Facts in its own words. An astrology source documents what astrologers believe or practise; it does not establish that astrology works.