Signs of equal power

Meaning

Two signs are of equal power when they lie the same distance on either side of a solstice: the start of Cancer, where the Sun reaches its furthest point north, or the start of Capricorn, where it reaches its furthest point south. Such signs are also said to behold, or "see", each other. Ptolemy counted the distance in whole signs; later authors count it degree by degree from the solstice point, which gives slightly different pairs (see below).

The Sun at 10° Taurus (about 30 April) and at 20° Leo (about 13 August) stands at the same height above the celestial equator. On both dates the day is the same length, and the Sun rises and sets at the same points on the horizon. Ptolemy gives both reasons: the equal days, nights and hours make the two places "of equal power", and rising and setting from the same part of the horizon is why they "behold" one another [1].

Measured degree by degree from the solstice points, the pairs are:

A degree's partner in the other sign is its antiscion. The two degrees always add up to 30 within their signs: 10° Taurus goes with 20° Leo, and 1° Gemini with 29° Cancer.

Origin and history

Ptolemy. The Tetrabiblos treats these signs in Book I, chapter 15 in Robbins's numbering, as one of the "familiarities" between signs besides the aspects [1]. (J. M. Ashmand's older English translation numbers the same chapter I.18 [5].) Ptolemy defines them as the parts equally removed from the same tropical sign. In the next chapter he calls signs disjunct or "alien" when they share none of these familiarities: not equal power, not commanding or obeying, and no aspect [1].

Ptolemy counts in whole signs. His translator lists the pairs as Gemini–Leo, Taurus–Virgo, Aries–Libra, Pisces–Scorpio and Aquarius–Sagittarius, each an equal number of signs from Cancer or Capricorn, with Cancer and Capricorn themselves left without partners [1]. This is not the same set as the table above. Ptolemy's reasons (equal days, same rising point) hold exactly only when you measure from the solstice point itself, degree by degree; that measurement produces the table's pairs.

Al-Bīrūnī. Writing in 1029, al-Bīrūnī uses the degree-by-degree scheme. Two signs that turn on the same parallel, north or south, because they are the same distance from a solstice, "correspond in course" (Wright adds the Latin in itinere). His examples are Gemini with Cancer and Taurus with Leo. Their day hours are equal, their night hours are equal, and the correspondence runs by inverse degrees [2]. He also reports that Abū Ma'shar treated some of these pairs as a softened kind of aspect. Gemini–Cancer and Sagittarius–Capricorn, neighbours that do not see each other in the ordinary way, he called "natural sextiles". Aries–Virgo and Pisces–Libra he called "natural opposites". And the square between Taurus and Leo, or Scorpio and Aquarius, loses its harshness through this bond [2]. Note that al-Bīrūnī's words differ from Ptolemy's: he keeps the word "power" for the pairs either side of an equinox (see commanding and obeying signs) [2].

Lilly. In English astrology the idea survives as the antiscion. Lilly, with a marginal reference to Ptolemy, defines the antiscion signs as those "of the same vertue", equally distant from the first degree of Cancer or Capricorn, in which the Sun makes days and nights of equal length [3]. He gives the example of 10° Taurus and 20° Leo, prints the table of pairs above, and finds the exact degree by subtracting the planet's degree from 30 [3]. Through its antiscion, he says, a planet gives influence to any planet or star that stands in that degree or aspects it. He likens the antiscions of the good planets to a sextile or trine, and the "contrantiscion", on the degree opposite, to a square or opposition [3].

Placidus. In 1657 Placidus tied the relation to actual declination. What are commonly called antiscia, he writes, he calls parallels, following Ptolemy's remark about signs on the same parallel: two bodies are in antiscion only when their declinations are equal, their latitude included. Pairs on the same side of the equator he calls primary or "beholding"; pairs on opposite sides are his secondary kind, where the northern commands and the southern obeys [4].

How it is used

Today the signs of equal power are met almost only as the antiscion, the mirror degree across the solstice axis; see antiscion for the technique. The companion relation across the equinox axis is described under commanding and obeying signs.

Because two ecliptic degrees of equal power stand at the same height above the equator, the relation is the ecliptic form of a declination parallel. The match is exact for points on the ecliptic, such as the angles, house cusps and lots. A planet with ecliptic latitude, the Moon above all, can sit on another's antiscion without being truly parallel.

On this site. The Antiscia panel works degree by degree, as Lilly does, not by Ptolemy's whole signs. It lists each point's antiscion (180° minus its longitude) and reports every point that sits on another's antiscion within the chosen orb (0.25° to 2°, 1° by default). For each contact it also says whether the two points are truly parallel in declination, and if not, names the points that lie off the ecliptic.

Examples

• The Sun at 10° Taurus and 20° Leo. Both have a declination of about 14°49′ north (with an obliquity of 23.44°), so days and nights are equal on the two dates. This is Lilly's own example [3].
• Saturn at 20°35′ Leo. Subtract from 30°: 9°25′. Its antiscion is 9°25′ Taurus [3].
• 15° Gemini and 15° Cancer. Each has a declination of about 22.6° north. Each is 15° from 0° Cancer, and the Sun takes about a month to pass from one to the other.
• Ptolemy's whole-sign pair Taurus–Virgo. 15° Taurus and 15° Virgo stand at about 16.3° and 5.9° north. Their days are far from equal, which shows why later writers turned to the degree-by-degree pairs.