What is an antiscium?
Draw a line through the tropical zodiac at 0° Cancer and 0° Capricorn. Reflect any planet's ecliptic longitude across that line and you have its antiscium. The paired signs are Aries–Virgo, Taurus–Leo, Gemini–Cancer, Libra–Pisces, Scorpio–Aquarius, and Sagittarius–Capricorn. Degree arithmetic is essential: a planet at 10° Aries reflects to 20° Virgo, not 10° Virgo. The two points sit an equal distance around the circle from the solstitial axis.
In absolute longitude from 0° Aries, the formula is antiscium = (180° − longitude) modulo 360°. “Modulo” means add or subtract a full 360° circle until the answer falls between 0° and less than 360°. The formula is its own inverse: reflect the antiscium again and the original longitude returns. Points exactly on 0° Cancer or 0° Capricorn reflect to themselves. This is a geometric property of the axis, not a special claim about a particular natal chart.
Contra-antiscia use the other axis
The contra-antiscium lies opposite the antiscium. Its longitude is (360° − original longitude) modulo 360°, which is the reflection across the Aries–Libra equinox axis. Continue the worked example: 10° Aries is absolute longitude 10°. Its antiscium is 180° − 10° = 170°, or 20° Virgo. Its contra-antiscium is 360° − 10° = 350°, or 20° Pisces. At 0° Aries the contra-antiscium is the original point and the antiscium is 0° Libra. Near the 0° Aries boundary, the modulo operation keeps the result within one zodiac circle.
What counts as a contact?
The site's pair table tests whether one body's mirror point is near another body's original tropical longitude. It tests mirrored conjunctions only. For a chosen orb of 1°, a distance of 0.80° is included and 1.20° is omitted. Angular distance always takes the shorter way around the circle: 359.8° and 0.2° are 0.4° apart, not 359.6°. An antiscia relation is reciprocal; if A's mirror is close to B, B's mirror is close to A by the same amount. The table therefore lists each unordered pair once. Self-contacts are omitted. Changing the orb does not change the calculated longitudes.
Birth time, zodiac, and interpretation
This calculator uses the tropical zodiac and apparent geocentric ecliptic longitudes for the Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. It does not include the Ascendant, houses, asteroids, or a sidereal reference frame. Planetary positions do not need a birthplace, but an accurate local time and historical UTC offset matter. If time is unknown, the tool takes a noon sample at the entered offset and labels it. The Moon can move far enough in a day to change its displayed mirror degree or a close contact; near a sign boundary, even a sign label may be uncertain.
Traditional astrologers may examine an antiscium as a subtle relationship between chart factors, but the historical literature is varied. A computed pair does not establish a person's character, a future event, or an inevitable relationship outcome. Read it beside the ordinary longitudes, aspects, house framework, and the source of the birth record. This guide supplies the arithmetic and uncertainty needed to compare that kind of table with a full chart.