For one day every year, most Christians (specifically Catholics and Lutherans, with a few other denominations) all over the world don an ash cross on their foreheads. Why?

Ash Wednesday is the start of Lent - a period of 46 days which consists of 40 days of fasting, with 6 Sundays of feasting. Lent is meant to observe both the 40 days that Jesus fasted in the desert, and the 40 years that the Israelites spent in exile after the Exodus. Lent ends on Easter, the celebration of Christ's resurrection from the grave.

The ashes, which are made from palm branches blessed on the previous year's Palm Sunday, represent the dust we came from, and the dust we'll return to.

While most western Christians don't actually fast, they do take this opportunity to give up something that they enjoy or hold dear.