Frequently asked questions
Understanding Astrology > Precession
Aries Pisces? Or what about the precession of the
The signs of the tropical zodiac, which starts at the Vernal Equinox with 0° Aries, are not the same as the fixed star constellations which carry the same names.
The signs are sections of the ecliptic circle, 30 degrees each. They serve as an abbreviated measurement system for ecliptic longitude relative to the true equinox of date. Instead of saying 'Saturn is at 123 degrees' we say 'Saturn is at 3 degrees of the 5th zodiac section'. Because the 5th zodiac section is named 'Leo', we say Saturn is at 3 Leo. We mean ecliptic longitude relative to the Equinox, so this is NOT the fixed star constellation Leo.
The fixed star constellations are irregular patches of stars on the sky. 2000 years ago those areas coincided roughly with the zodiac sections, and that is where they got their names from. The fixed star constellations are not used for measuring coordinates of objects on the sky.
Due to the effect of lunisolar precession, the ecliptic circle has since shifted versus the fixed star background, and continues to shift by 1° every 72 years.
Astronomers, who often hate astrology, love to confuse people by pretending of not being aware of the difference between fixed star constellations and the reference frame of the tropical ecliptic coordinate system. In fact, astronomy uses the very same ecliptic coordinate system as astrology does. Also astronomers give the position of objects in the ecliptic by measuring the longitude from the Equinox. Some astronomers try to make astrologers look stupid, when in fact all they manage is confusion of the "innocent public".
For further information, please read Precession and Zodiac or the full documentation of Swiss Ephemeris.
astrologers use the sidereal zodiac as well?
In Indian (Hindu / Vedic) astrology, the sidereal zodiac is used. The precession of the equinox is not taken into account there. Western astrology only refers to the sidereal zodiac in connection with the world ages, like the Age of Aquarius or the Age of Pisces.