Diëteris

A diëteris or biëteris is the Greek name for the period over 2 tropical years where the Moon phase occurs around 8 years later.

It corresponds to 25 synodic months,

2.0213017935214 sidereal months, 27.129896020025 draconic months, 26.792841801954996 anomalistic months, and 738.264699074075 days.

It’s the result of intercalating 2 lunar years (which’s 24 synodic months, 1.9404497217805439 sidereal months, 26.044700179224 draconic months,

25.721128129876796, and 708.734111111112 days).

It approximates 2 synodic periods of Uranus, meaning 2 new/full moons in opposite/conjunction with Uranus occur a diëteris apart.

Though adding an extra synodic month forms a long diëteris, which is 28.1020710232132 sidereal months, 28.215091860826 draconic months, 27.864555474033196 anomalistic months, and 767.7952870370381 days, and is sometimes useful for calculating oppositions with Mars.