A lunation is the interval of time between two new moons or two full moons. The lunation is used as a reference in lunar calendars such as the Hijri calendar for example. The duration of a lunation is sometimes abbreviated by a 29 1/2 or 29.5 on moon phase displays. The reality is much more accurate. It is 29 days 12 hours 44 minutes 2.8 seconds or 29.530587963 days.