Ash Wednesday, in Western Christianity, the first day of Lent, occurring six and a half weeks before Easter (between February 4 and March 11, depending on the date of Easter). Ash Wednesday is a solemn reminder of human mortality and the need for reconciliation with God and marks the beginning of the penitential Lenten season. It is commonly observed with ashes and fasting. Eastern Orthodox churches begin Lent on Clean Monday and therefore do not observe Ash Wednesday.
In the early Christian church, the length of the Lenten celebration varied, but eventually it began 6 weeks (42 days) before Easter. This provided only 36 days of fasting (excluding Sundays). In the 7th century, 4 days were added before the first Sunday in Lent in order to establish 40 fasting days, in imitation of Jesus Christ’s fast in the desert.
It was the practice in Rome for penitents and grievous sinners to begin their period of public penance on the first day of Lent in preparation for their restoration to the sacrament of the Eucharist. They were sprinkled with ashes, dressed in sackcloth, and obliged to remain apart until they were reconciled with the Christian community on Maundy Thursday, the Thursday before Easter. When these practices fell into disuse (8th–10th century), the beginning of the penitential season of Lent was symbolized by placing ashes on the heads of the entire congregation.
In the modern Roman Catholic Church, the ashes obtained by burning the palms used on the previous Palm Sunday are applied in the shape of a cross on the forehead of each worshiper on Ash Wednesday. The ashes serve as a memento mori and are often accompanied with some variation of the words, “Remember that you are dust, and to dust you shall return.” Together with Good Friday (which marks the crucifixion of Jesus before Easter), Ash Wednesday is an obligatory day of fasting and abstinence, where only one full meal and no meat are to be consumed. Although Ash Wednesday is not a holy day of obligation, it is traditionally one of the most heavily attended non-Sunday masses of the liturgical year. Worship services are also held on Ash Wednesday in Anglican, Lutheran, and some other Protestant churches.
Britannica, T. Editors of Encyclopaedia. “Ash Wednesday.” Encyclopedia Britannica, Invalid Date. https://www.britannica.com/topic/Ash-Wednesday-Christian-holy-day.