I was inspired a little while back to devise a new metrical form, structured according to the Metonic cycle. Simply put, the Metonic cycle (observed by Meton of Athens) is “A period of 235 lunar months, or about 19 years in the Julian calendar, at the end of which the phases of the moon recur in the same order and on the same days as in the preceding cycle.” (definition from American Heritage dictionary) Each year is divided into 12 lunar months; every few years a 13th month is added to bring the lunar and tropical (seasonal) cycles back into harmony, so that November doesn’t wind up coming in the spring :).
In this scheme, the years 3, 6, 8, 11, 14, 17, and 19 are the long (13-month) years; I have seen that there were slight variations in this arrangement in different places, but since this pattern (a) was the most common, and (b) corresponds to the only (AFAIK) Metonic calendar still in active use (the Jewish calendar), I’ll go with it.
My new poetic form, then, has 19 lines of 12 metric feet each, with a 13th foot added in lines 3, 6, 8, 11, 14, 17, and 19. I haven’t decided about meter or rhyme; I may not try to define them at this point, but experiment with writing in the form and see what happens – and I invite anyone with an interest to do so as well! If you do write something in this form, please consider sharing the results – I’d love to see it.
For really hardy souls, there is also the Calippic cycle, which was proposed in the century following Meton as an improvement on his calendar; the Calippic Cycle is basically four Metonic cycles (minus one day dropped from the last cycle), an arrangement that was intended to bring everything back to true alignment with the actual natural cycles – although according to the article it doesn’t, really.
Poetically, I envision a Calippic cycle as either a series of four related Metonic poems or one long poem in four parts, that at the end returns to and works a slight change on the beginning (thematically as well as in the matter of one dropped foot in the last Meton).