Ash Wednesday, a day of fasting, is the first day of Lent in Western Christianity. It occurs 46 days before Easter and can fall as early as 4 February or as late as 10 March. Ash Wednesday is observed by many Western Christian denominations.
According to the canonical gospels of Matthew, Mark and Luke, Jesus Christ spent 40 days fasting in the desert, where he endured temptation by Satan. Lent originated as a mirroring of this, fasting 40 days as preparation for Easter. Every Sunday was seen as a commemoration of the Sunday of Christ's resurrection and so as a feast day on which fasting was inappropriate. Accordingly, Christians fasted from Monday to Saturday (6 days) during 6 weeks and from Wednesday to Saturday (4 days) in the preceding week, thus making up the number of 40 days.
Ash Wednesday derives its name from the practice of blessing ashes made from palm branches blessed on the previous year Palm Sunday, and placing them on the heads of participants to the accompaniment of the words "Repent, and believe in the Gospel" or "Remember that you are dust, and to dust you shall return".

Mardi Gras, also Fat Tuesday in English, refers to events of the Carnival celebrations, beginning on or after the Epiphany or King's Day and culminating on the day before Ash Wednesday. Mardi Gras is French for "Fat Tuesday", reflecting the practice of the last night of eating richer, fatty foods before the ritual fasting of the Lenten season.

Although most modern calendar years have 365 days, a complete revolution around the Sun (one solar year) takes approximately 365 days, 5 hours, 48 minutes, and 46 seconds (or, for simplicity's sake, approximately 365 days and 6 hours, or 365.25 days).[5] An extra 23 hours, 15 minutes, and 4 seconds thus accumulates every four years (again, for simplicity's sake, approximately an extra 24 hours, or 1 day, every four years), requiring that an extra calendar day be added to align the calendar with the Sun's apparent position. Without the added day, in future years the seasons would occur later in the calendar, eventually leading to confusion about when to undertake activities dependent on weather, ecology, or hours of daylight.