Orb

Meaning

Two planets are rarely at an exact aspect. The orb (Latin orbis, "circle") is the margin allowed on either side of exactness within which the aspect is still said to be in force. A square is exact at 90°; with an orb of 5°, anything from 85° to 95° is counted as a square.

Orbs answer a practical question, but they also carry an idea: that an aspect has a centre of strength which fades with distance, so that a close aspect matters more than a wide one. Different traditions have put the margin in different places and made it depend on different things: on the planet, on the aspect, or on the technique being used.

Origin and history

Ptolemy. The Tetrabiblos defines the aspects by the figures they make, counted in signs and in degrees (opposition six signs or 180°, trine four signs or 120°, square three signs or 90°, sextile two signs or 60°), and gives no table of orbs (I.13) [1]. When Ptolemy discusses planets applying to and separating from one another, he says only that the interval between them should not be great, without a number; Robbins notes that an anonymous ancient commentator gave 15° as the maximum distance (I.24) [1].

Orbs of the planets and moieties. In the astrology that came down through Arabic and Latin authors, each planet was given its own orb, the distance within which its influence reaches another planet, of a set number of degrees. Al-Bīrūnī's table (1029) gives, for example, Saturn and Jupiter 9°, the Sun 15°, Venus and Mercury 7°, the Moon 12°; his translator notes that the same figures are found in Porphyry (3rd century) and that later books vary them (§ 436) [3]. Among the opinions he reports on when an application begins is one that takes half the sum of the two planets' orbs (§ 490) [3]. Lilly states this as the rule: each planet is allowed half its own orb and half the other's (p. 110) [2]. Each half is the planet's moiety (from the French for "half"). His example: Venus in 10° Taurus and Saturn in 18° Virgo are 8° from an exact trine; the moiety of Saturn's orb is 5° and of Venus's 4°, so Venus is within the moieties of both and the trine is in force, as a "platic" (wide) aspect (p. 107) [2].

Lilly's table, printed with that example, gives the planets' orbs, with the smaller figures other authors used (p. 107) [2]:

The luminaries have the largest orbs; slow Saturn and Jupiter come next; Mars, Venus and Mercury have the smallest. Lilly adds that he sometimes uses the one column and sometimes the other. The "others" column is close to al-Bīrūnī's figures.

Modern practice. Most modern astrologers attach the orb to the aspect rather than to the planet: larger for conjunctions and oppositions, smaller for sextiles and the minor aspects, often with extra room when the Sun or Moon is involved. The actual figures differ widely from one author and one computer program to another, and there is no agreed standard.

Ebertin. Reinhold Ebertin, the founder of cosmobiology, kept orbs by the kind of point rather than by the aspect. For aspects he adopted 5° for the personal points (Sun, Moon, Midheaven, Ascendant), 4° for Mercury, Venus and Mars, and 3° for Jupiter to Pluto and the Moon's Node, figures taken from his earlier book Die kosmischen Grundlagen unseres Lebens. His reasoning was that the personal points deserve the most room and the slow planets the least, since their positions are shared by very many people. He rejected the traditional orbs of up to 15° as untenable (pp. 22, 199) [5].

How it is used

Orbs in midpoint work. Techniques built on midpoints use much smaller orbs than ordinary aspects. A planet has to fall within about 1° to 2° of a midpoint, not 5° to 10°, before a planetary picture is recognised. Reasons offered include that a midpoint involves three factors at once, and that on a folded dial a wide orb would bring in contacts by chance.

• Birth charts. Ebertin allows an orb of only 1½° for midpoints. If a contact is doubtful the pointer of the dial may be moved up to 1½° either side, but no further; an orb of 3° is too large. He adds that readers should test this for themselves rather than argue over rules (pp. 23, 27, 199) [5]. 1½° is also a common default in midpoint software. Other writers use figures between about 1° and 2°, and some allow only about 1° when the planet reaches the midpoint by aspect rather than by conjunction [4].
• Directions and transits. Timing work uses tighter orbs still. Ebertin allows at most 1° for transits, and says the effect of directions and transits is limited to about one degree either side (pp. 69, 107) [5]. A solar arc direction moves about a degree a year, so the orb is in effect a window of time. Ebertin allowed a little more for contacts to the Ascendant and Midheaven when the birth time might be slightly wrong (p. 89) [5].
• Weighting. Within the orb the closest contacts are read first; a picture exact to a few minutes of arc is given more weight than one at the edge.

Folding onto a dial does not change the size of an orb. One degree of the zodiac is one degree on the 90° dial, even though the dial is drawn four times larger.

On this site. In the Midpoints panel the orb is a slider from 0.5° to 3°, default 1.5°, and applies to every planetary picture and tree, and to the dial pointer, measured on the chosen dial. Midpoint clusters use a fixed 1° spacing between neighbouring midpoints. The cazimi and combust limits are separate fixed distances, not orbs in this sense.

Examples

Albert Einstein (14 March 1879, 11:30 local mean time, Ulm).

• Sun and Mercury. The Sun is at 23°30′ Pisces and Mercury at 3°09′ Aries, 9°38′ apart. By Lilly's moieties (half of 17° plus half of 7°, that is 12°) they are conjunct. A modern author using, say, a 6° orb for conjunctions would not count it.
• Sun and Saturn. Saturn at 4°11′ Aries is 10°41′ from the Sun, again within Lilly's moieties (8°30′ plus 5°, 13°30′).
• A midpoint at the edge. Saturn is 1°03′ from the Sun/Venus midpoint (5°15′ Aries). With the default 1.5° it appears as the second branch of Saturn's tree; with an orb of 1° it disappears, leaving only Saturn = Uranus/Neptune at 0°23′.