A 45° angle — half a square, and one of the aspects Johannes Kepler argued into astrology in Harmonices Mundi (1619) from harmonic ratios rather than from sign relationships. It belongs to the square family and behaves like a square kept indoors: real friction, held internally, expressed as irritation rather than crisis.
A semi-square transit builds tension without giving it anywhere to go. The natal point is chafed rather than challenged — a slow accumulation of annoyance that becomes obvious only when it finally discharges, often at the square or sesquiquadrate that follows in the same cycle.
Transit Mars semi-square natal Mercury shortens the fuse in conversation — nothing erupts, but everything said takes more effort to keep civil.
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