Lunar year
Appearance
![](http://upload.wikimedia.org/wikipedia/commons/thumb/c/c0/Lunar_libration_with_phase2.gif/220px-Lunar_libration_with_phase2.gif)
A lunar year (used in some calendars) of 12 synodic months (12 cycles of lunar phases) is about 354 days long. A cosmic year is the time (about 225 million years) needed for the solar system to revolve once around the centre of the Milky Way.