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Jae C. Hong, Associated Press
Students attend an Ash Wednesday Mass at Santa Margarita Catholic High School on Wednesday, March 5, 2014, in Rancho Santa Margarita, Calif. Ash Wednesday marks the beginning of Lent, a time when Christians commit to acts of penitence and prayer in preparation for Easter Sunday.

Millions of Christians around the world will be seen with ashes in the form of a cross on their foreheads Wednesday as they celebrate the first day of Lent.

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Ash Wednesday, as it is called, is 46 days before Easter, which includes six Sundays. For Christians, so begins a 40-day period of prayer and fasting, or abstaining from a particular food they like; The six Sundays during this are not included in the fasting period.

Ashes are placed on the forehead as a reminder of mortality and repentance of sins. As a sign of their faith, many Christians leave them on all day. A photo gallery showcasing a handful of Ash Wednesday services and images from around the world can be seen above.