Threads of Invasion
In Eberron, there are 12 months in a year, and 28 days in a month. As well as representing the passage of the seasons, each month is tied to its own moon, and a specific dragonmark.
For a whizzy cosmology and calendar tool, click here. As well as giving you the phase of each moon depending on the date, that tool will tell you which planes are waxing, waning, remote or coterminous.