Inter-aspect

Meaning

An inter-aspect is an aspect between two charts: a planet in one person's chart and a planet in the other's. It is measured exactly as an aspect inside one chart. Take the two zodiac longitudes, find the shorter distance between them (0° to 180°), and see whether that distance is close to one of the aspect angles: 0° conjunction, 60° sextile, 90° square, 120° trine, 180° opposition, and the minor aspects if they are used. How far the distance is from the exact angle is the orb of the contact.

Inter-aspects are the main material of synastry. The other main tools are the house overlay, which places one person's planets in the other's houses, and the charts made for the pair.

The same angle both ways. The distance between two points does not depend on which one you start from, so the measurement is symmetric: "his Sun square her Mercury" and "her Mercury square his Sun" are one contact, and it is listed once. What is not symmetric is whose planet is whose. His Sun on her Mercury is a different contact from her Sun on his Mercury, and the two need not be in aspect at all (see the examples).

No applying or separating. Inside one chart, or between a moving planet and a birth chart, an aspect is applying while the faster planet approaches the exact angle and separating once it has passed. Between two birth charts both positions are fixed, each at its own moment of birth, so nothing approaches anything. Any sense of one person's planet acting on the other's belongs to the interpretation; the geometry itself has no direction.

Origin and history

Ptolemy compares planets across two charts in the Tetrabiblos. For marriage he looks at the Sun and Moon of both charts: harmony by trine or sextile, especially "by exchange", makes for lasting marriages, and even more so when the husband's Moon is in such an aspect to the wife's Sun; the luminaries in disjunct signs, in opposition or in square point to separation [1]. Robbins's note explains "exchange", after the ancient commentator, as the luminaries of one chart aspecting those of the other: Sun with Sun, Moon with Moon, or Sun with Moon each way [1]. For friendship and enmity he compares the Sun, Moon, Ascendant and Lot of Fortune of both charts: in the same signs or in exchange they make firm sympathy, in disjunct or opposite signs enmity; trine and sextile make the sympathy less, and square the enmity less [1]. Two points stand out. Ptolemy works mostly by sign (same signs, disjunct signs) rather than by orb, and he gives the partners' roles weight: the husband's Moon to the wife's Sun is singled out, not the other way round.

Modern synastry extends the comparison to every planet and to the angles, and measures aspects by degree with an orb, as in natal work. Ronald Davison's Synastry (1977) lists "planetary cross aspects" among its methods of comparison, according to its publisher [4]. Reinhold Ebertin, in Applied Cosmobiology (1972), takes the cosmobiological approach: both charts on the 90° dial, where conjunctions, squares and oppositions fall on the same spot, with one person's planets read against the other's planets and midpoints; he refers readers to his The Contact Cosmogram (1974) for many more examples [2] (see contact cosmogram).

How it is used

Which contacts count most. Following Ptolemy, the Sun and Moon of each chart come first [1]. Ebertin's list of factors to watch between partners goes on to Venus and Mars, then Jupiter, Saturn, the outer planets and the Node [2]; the Ascendant and Midheaven are added when birth times are known. The pairings in Robbins's note, Sun with Sun, Moon with Moon and each Sun with the other's Moon, are the classic ones; like with like (Venus with Venus) extends the same idea [1].

Orbs. There is no settled standard. Ptolemy speaks mostly of signs, not degrees [1]. Modern astrologers often use orbs like those of the natal chart, or somewhat smaller. Cosmobiologists work much tighter. Ebertin insists that contacts between partners' charts be almost exact: since he allows a transit at most 1°, a transit can set off both charts together only when their contact is within that 1° limit [2].

Unknown birth times. An inter-aspect needs only the two positions. For the slow planets the date is enough. The Sun moves about 1° a day, Venus up to about 1¼° and Mercury up to about 2°, so their orbs are uncertain by up to a degree or so either way. The Moon moves 12° to 15° a day, so without a birth time a Moon contact may or may not be within orb, and its exact orb is unknown.

On this site. The Contacts tab of the Synastry tool lists every inter-aspect between the two charts once, as the first person's planet, the aspect and the second person's planet, closest first. The planets from the Sun to Pluto and the Moon's true Node are compared; the mean Node and Lilith are left out. Each card shows both positions, how far the aspect is from exact, and its class: major, common minor or extended minor. A filter shows the majors only (the default), the majors and common minors, or all aspects. Orbs depend on the aspect, not the planet: 8° for the conjunction and opposition, 7° for the square and trine, 5° for the sextile; 3° for the quincunx; 2° for the semi-sextile, semi-square, sesquiquadrate, quintile and biquintile; 1° to 1½° for the extended minors. The same contacts are drawn as lines across the double wheel. Applying and separating are not shown. When a birth time is unknown, that person's Moon is marked approximate. The Contact cosmogram tab shows the hard contacts, and each person's planets on the other's midpoints, on a 90° dial (a 45° or 360° dial can be chosen; orb 1° by default, adjustable from ¼° to 2°), and the Mirrors and parallels tab adds contacts by antiscion and declination parallel.

Examples

Albert Einstein (14 March 1879, 11:30 local mean time, Ulm; 10:50:02 UT) and Mileva Marić (19 December 1875, Titel). Mileva's birth time is not recorded; Astro-Databank gives about 10 a.m., estimated from a narrative in a biography [3]. Her chart here is cast for noon local mean time (10:38:48 UT), and the range over her whole birth day is given where it matters. Orbs as on this site.

• Sun square Mercury. Einstein's Sun at 23°30′ Pisces (353.508°) and Mileva's Mercury at 23°16′ Sagittarius (263.269°) are 90.239° apart: a square, 0°14′ from exact. Counted from her Mercury to his Sun the distance is the same. Over her birth day the orb runs between 0°00′ and about 1°01′, so the square is certain.
• The reverse pair is different. Einstein's Mercury (3°09′ Aries) and Mileva's Sun (27°10′ Sagittarius) are 95°58′ apart: a square 5°58′ wide, within the 7° orb but far looser.
• Jupiter sextile Sun. Einstein's Jupiter at 27°29′ Aquarius and Mileva's Sun: 60.312°, a sextile 0°19′ from exact (0°00′ to 0°49′ over her birth day).
• Saturn conjunct Node. Einstein's Saturn at 4°11′ Aries and Mileva's Node at 4°31′ Aries: 0°20′, the same at any hour.
• Like with like. Einstein's Venus (16°59′ Aries) squares Mileva's Venus (18°47′ Capricorn), 1°48′ from exact.
• A Moon contact. Einstein's Pluto (24°44′ Taurus) trines Mileva's noon Moon (25°04′ Virgo), 0°21′ from exact. Over her birth day the orb could be anything from 0°00′ to 6°42′: the trine is there on any hour (the orb is 7°), but how close it is cannot be known.