In 2014, Christmas fell on a Thursday, the start of Hanukkah fell on a Wednesday and the start of Passover fell on a Tuesday. Ramadan began on a Saturday, Eid-al-Fitr (the end of Ramadan) fell on a Monday, and Diwali, the Hindu Festival of Lights, fell on a Thursday.
Many religious holidays occur on a specific date. Christmas, for example, is always on Dec. 25. However, the day of the week Christmas falls on moves forward a day each year and two days each leap year.
The date of Ramadan is determined each year based on the ninth month of the Islamic calendar. Because the Islamic calendar is lunar-based, the date varies each year when translated to the Gregorian solar-based calendar. Similarly, Diwali always occurs on the darkest new moon night in the Hindu month of Kartika. This day corresponds to some day between mid-October and mid-November.
Other holidays, such as Easter Sunday, Ash Wednesday and Good Friday, fall on the same day of the week every year, but the date on which they occur varies. Easter Sunday's date is calculated based on a complex formula centered around the Spring Equinox. Once the date of Easter Sunday is determined, its associated holidays' dates can be calculated. For example, Good Friday is the Friday before Easter Sunday, and Palm Sunday is the Sunday before Easter.