Resonance between lunations and anomalistic months is also important. This discusses the 206-day cycle in eccentricity. Low perigee values occur alternately at Full Moon and New Moon, so the complete double-cycle is the one associated with variations in lunation length. This describes the 8.85-year cycle. Based on New Moon birth in UT, Islamic dates were calculated for 1416 to 1419 H, and past and future instances of four successive 30-day months were tabulated.
Diagrams illustrate the ecliptic and the effect of lunar latitude.
Bradley E. Schaefer. The grey area between success and failure is amply illustrated. Detailed crescent observations are tabulated in this and in earlier references. Willmann-Bell Inc., Richmond, Virginia, 1991. Chapters 47 and 48 discuss the lunar orbit.