Gyroscope spin axis precession from parallel transport in curved spacetime
Geodetic (de Sitter) precession: a gyroscope in circular orbit at r precesses by Ω_geo = (3/2)(GM/c²r)·v_orb per radian. For Earth orbit (r≈6700 km) this gives ~6.6 arcsec/yr, confirmed by Gravity Probe B (2011) to 0.28%. The effect arises because orbital angular momentum and spin are parallel-transported on a non-flat path — the Fermi-Walker transport equation governs the spin 4-vector.