# Semi-square: the 45° minor aspect in a birth chart > What a semi-square is in astrology: the 45° angle, the square family, a 1-2° orb, its role in cosmobiology and the Hamburg School, and how to read it. URL: https://kb.astroway.info/en/aspects/semisquare A semi-square is an aspect between two planets that stand 45° apart along the ecliptic. It is half a [square](/en/aspects/square) and one eighth of the circle, which is why it is also called an octile. The semi-square is a minor aspect, but not a random one: together with the sesquiquadrate it forms a family of hard aspects that grows out of dividing the circle by four and by eight. ## Geometry: half a square Where the square divides the circle into four, the semi-square divides it into eight. Hence the direct link: two planets in semi-square stand as a planet does to the midpoint of a square. Add 90° to 45° and you get 135°, the [sesquiquadrate](/en/aspects/sesquiquadrate). Together with the conjunction (0°), square (90°) and opposition (180°), these angles form the series of multiples of 45°. Astrologers who work with harmonics call it the eighth harmonic and read it as an axis of tension and action. A distance of 45° equals a sign and a half, so the semi-square, unlike the major aspects, is not tied to a pair of signs. A planet at 5° Aries is in semi-square to one at 20° Taurus, while a planet at 25° Aries is in semi-square to one at 10° Gemini. The signs may be neighbours or one sign apart, and nothing about element or modality can be said in advance. ## Where the aspect comes from Ptolemy did not know the semi-square. Aspects in multiples of 45° entered practice with the other minor aspects, once the angle between planets came to be measured exactly rather than by sign. Two 20th-century schools gave them particular weight. The Hamburg School, founded by Alfred Witte early in the century, and the cosmobiology of Reinhold Ebertin that grew out of it, worked with a 90° dial. On such a dial the conjunction, square and opposition fall on one point, while the semi-square and sesquiquadrate land exactly opposite. For these schools the 45° series was the main working tool, and in their practice a semi-square weighs almost as much as a square. ## The orb of a semi-square In ordinary natal practice the semi-square gets a narrow [orb](/en/aspects/orbs): 1-2°, up to 2-3° with the Sun or Moon. The schools that use the 90° dial are stricter still, often allowing no more than 1-1.5°. With a wide orb, every chart holds several semi-squares and the aspect stops meaning anything. ## How to read a semi-square The semi-square shares the character of the square, only weaker and less visible from outside. A square often describes an open conflict the person knows about. A semi-square describes friction that builds up little by little: irritation, impatience, a sense that two parts of life get in each other's way, with no open crisis. Modern writers also link it to motivation: a small tension that keeps a person from standing still. The order of reading is the usual one: - **Planets.** Which functions are under tension. A semi-square of the Sun to Mars speaks of will and action; one of Mercury to Uranus, of thinking and sudden change. - **Signs.** How each planet acts. Since the signs can be any, look at each planet on its own rather than searching for a shared element. - **Exactness.** A semi-square within 1° deserves attention, especially if a luminary takes part. Like any minor aspect, the semi-square should not be the basis of a conclusion about a chart. It refines rather than defines. ## Example: the semi-square in Zendaya's chart In [Zendaya's chart](/en/people/zendaya) the Sun is at 9°50′ Virgo and Mars at 25°04′ Cancer. The angle between them is about 44°46′, an orb of 0°14′. Cancer and Virgo are one sign apart, so by sign they form a sextile, yet the exact angle gives a semi-square: a good illustration that eighth-harmonic aspects ignore sign boundaries. The Sun forms an almost identical semi-square to Venus at 24°33′ Cancer, with an orb of 0°16′. Tradition would read such a pair as tension between will and desire that does not surface as open conflict but asks for constant small corrections. This describes a link between functions of the chart, not a judgement of the person. ## How to find a semi-square in your own chart Most software leaves minor aspects out of its tables, so a semi-square often has to be found by hand. Convert the planets' positions to absolute degrees: Aries 0-30°, Taurus 30-60°, Gemini 60-90° and on around the circle to Pisces at 330-360°. Zendaya's Sun at 9°50′ Virgo becomes 159°50′, her Mars at 25°04′ Cancer becomes 115°04′. For each pair, subtract the smaller number from the larger; if the result is over 180°, subtract it from 360°. An angle within 1-2° of 45° is a semi-square. You cannot spot it by sign: 45° is a sign and a half, so the two planets' degrees within their signs differ by about 15°. If one planet sits at 10° of a sign, look for a semi-square partner near 25° of the next sign, or near 25° of the sign two places back. ## Semi-squares in configurations On their own, semi-squares rarely build well-known figures. The nearest relative is the figure known as Thor's hammer or the fist of God: two planets in square and a third in sesquiquadrate to both. The point opposite the apex of this figure lies at the midpoint of the square and stands in semi-square to both its ends, so the whole figure is built from multiples of 45°. The section has no separate page for it yet. The classic configurations made of major aspects are covered under [aspect patterns](/en/aspects/patterns).