@frameacloud Chinese zodiac, cycles through itself every 12 years (and through all combinations of signs + associated elements every 60).
@frameacloud Ah, makes sense! Hmmm.
The sun, the moon and the Earth take roughly 18 years to return to (more or less) the same positions; this is used to predict eclipses.
@Thaminga
Oh yeah, that's a good one! Astrology is great for cycles. For my project, I'm trying to not use anything astrological, but astronomical is good.