In astronomy, a lunar fortnight is half a lunar synodic month, which is equivalent to the mean period between a full moon and a new moon (and vice versa). This is equal to 14.07 days.[3][4] It gives rise to a lunar fortnightly tidal constituent (see: Long-period tides). In many languages, there is no single word for a two-week period, and the equivalent terms "two weeks", "14 days", or "15 days" (
