A lunar calendar is a calendar oriented at the moon phase. This is normally done by having a month which corresponds to a lunation so that the day of month indicates the moon phase. If a calendar tracks the seasons, it is also a lunisolar calendar. Since there are about twelve lunations (synodic months) in a solar year, this period (354.37 days) is sometimes referred to as lunar year, corresponding to thirteen sidereal months (355.18 days).