A similar calculation shows that the Earth had exerted angular momentum through tidal friction on the Moon self-rotation, before this became tidally locked. At that period, one calculates the change in the Moon angular momentum "ω" in the same manner as for "Ω" above, except that "m" and "M" should be is switched, and "A" should be replaced by the Moon radius "a" = 1.7×106 meter. Taking formula_29 of 10−1 — 10−2 as for the solid planets and "k" = 1, this gives the deceleration of the Moon's rotation d"ω"/d"t" = -3×10−17 — −3×10−18 radian sec−2. For a 29.5-day long rotation period, this is equivalent to 1.5 – 15 minutes in 1 year, or 1 day in 102 — 103 years. Thus in astronomical timescales, the Moon became tidally locked very fast.