A
lunisolar calendar is a
calendar in many
cultures whose date indicates both the
moon phase and the time of the solar
year. If the solar year is defined as a
tropical year, then a lunisolar calendar will give an indication of the
season; if it is taken as a
sidereal year, then the calendar will predict the
constellation near which the
full moon may occur. Usually there is an additional requirement that the year have a whole number of months. In this case ordinary years consist of twelve months but every second or third year is an
embolismic year , which adds a thirteenth
intercalary, embolismic, or leap month.