Effect of the moon in the determination of latitude at Washington

Observations taken with the photographic zenith-tube of the United States Naval Observatory for the determination of latitude during the 24-year period 1915.9 to 1939.9 were examined for lunar terms. The effect of the Moon was assumed to be Δϕ = A 2 cos 2t + B 2 sin 2t + A 1 cos t + B 1 sin t (1) where Δ ϕ is the effect on the observed latitude, t is the Moon's hour-angle, and A 2, B 2, A1, B1 are constants to be determined.