NOTE: Some dates are approximate, since they are based on complicated astrological or liturgical calculations, or the time when the new moon is actually sighted in certain areas. Different tribes, villages or groups may celebrate the same holiday on two or three different dates. There is also great variation in the number of days some events are celebrated. Some holidays combine ceremonies from more than one religion or culture. Also the phenomenon of the "International Dateline" can cause an event (even one based on an exact astronomical moment) to be celebrated on two different days in different locations.