← Encyclopedia of Astrology · lesson 100/235
Semi-square
A semi-square (also octile) is two planets 45° apart — an eighth of the circle, the eighth harmonic, made by halving the square. Because 45° is a sign and a half, it has no fixed sign relationship: it may join neighbouring signs or signs two apart, depending on where in the signs the planets fall. It belongs to the minor aspects Kepler added to Ptolemy's five, and Robert Hand treats it, with the sesquiquadrate, as part of the same family of hard aspects as the square.
Its character is friction at low volume. Where a square confronts, a semi-square irritates, nags and prods: a persistent, slightly unsettling pressure that is easy to put up with and hard to ignore for long. Because it does not fully block, it often prompts small, repeated efforts — and can be a quiet engine of drive.
Orb
Minor aspects are kept tight in nearly every tradition, usually 1–2°. In the charts here the semi-square is capped at 2°; the bodies' own allowances only matter if they are tighter still. Its strength is how tight it is against that allowance, 1 at exact and 0 at the edge. See orb.
Ease or tension
The semi-square counts as tension in the ease and tension chart, at under half the weight of a square. It inclines toward irritation and restlessness, the kind that can be turned into persistence.
In a chart
Read it like a square in a lower key: what does each planet want, and where do they keep catching on each other? Mars semi-square the Sun might show impatience that flares easily and fuels a lot of work. Semi-squares and sesquiquadrates joining the ends of two oppositions form a hard rectangle.
In transit
The transit lists here follow the major aspects with the quincunx and semi-sextile, so transiting semi-squares are not listed; many astrologers who do use them treat them as brief, minor triggers.
Kinds and conditions
- Applying or separating, like any aspect.
- Waxing (45° after a conjunction) and waning (45° before the next one) semi-squares are sometimes read separately: the first a push to get going, the second a push to let go.
- Being a sign and a half, it has no "in-sign" form, so the idea of out-of-sign does not really apply.