Anyone unfamiliar with certain religious practices may notice something special about the day after Mardi Gras.

On Ash Wednesday every year, those who celebrate the season of Lent will visit their churches early in the morning. There, a priest uses ashes to mark a sign of the cross on their foreheads, leaving a black mark that remains for the rest of the day.

The custom made headlines last year when U. S. Vice President Joe Biden appeared on television with a smudge on his forehead. This time, the gaffe-prone politician wasn't the one with his foot in his mouth.

What's happened to his head? said anchorwoman Kay Burley during a live broadcast of Sky News in the UK, It looks like he's walked into a door!

Some viewers were offended, and Burley had to make a public apology. Don't let the same thing happen to you--here are five important facts about Ash Wednesday and the traditions behind it.

It's the Beginning of a Long 40 Days

Fat Tuesday, which precedes Ash Wednesday, is a legendary day of excess for good reason: it's the last hurrah before a 40-day period of fasting known as Lent. Not all churches count those 40 days in the same way -- most Western churches exclude Sundays, while Eastern churches do not. Nor does everyone fast to the same degree. For many Americans, Lent is a time to give up a single indulgent item. But some of the more traditionally-minded believers engage in more severe fasting and refrain from all celebrations.

It's Rooted in Biblical Tradition

Easter Sunday is a celebration of the resurrection of Jesus after his crucifixion. The Lenten period, which directly precedes Easter, commemorates the events leading up to his death. By fasting, believers hope to replicate that period of their savior's suffering.

The length of Lent reflects the recurrence of 40-day periods throughout the Bible. The flood of Genesis lasted for just that amount of time. Moses fasted for 40 days before receiving the commandments, and Jesus did the same to prepare himself for ministrations.

The Ashes Come from Last Year's Palm Tree

The smudges that appear annually on the foreheads of believers traditionally come from the ashes of a palm tree burned on Palm Sunday of the year before.

But all is not lost if you've misplaced the palm ashes from last year--these days, churches don't have to go the traditional route. They can purchase the necessary supplies online, even on rush order. Commercial palm growers in southern states this year sold packets of ashes for about $10 an ounce, and many of them ran out of inventory days ago.

The Exact Origin of the Ritual is Unclear

In the Bible, there are instances where ashes are associated with mourning, including Jonah 3:6, Esther 4:1 and Isaiah 15:3.  This ties into the notion that today's Lent participants are mourning the period of Jesus' suffering.

But the specific habit of applying ash on the face has debatable roots. Some say that any mark on the forehead is a symbol of ownership throughout the Bible, so this placement signifies obedience to the teachings of Jesus. Others have traced the ritual all the way back to ceremonies of the ancient Vedic Hindus, arguing that it was eventually absorbed into Christian lore.

There's No Obligation

Unlike some other major holidays, Ash Wednesday is not a Holy Day of Obligation. In other words, believers don't have to go to church; they are only encouraged to do so in order to properly mark the beginning of Lent.

According to the Code of Canon Law, a guide set out by the Vatican, On Sundays and other holy days of obligation, the faithful are obliged to participate in Mass. Ash Wednesday is not included as a holy day. It is, however, a day of required abstention from meat and general fasting -- that's a reduction rather than cessation of consumption -- for anyone between the ages of 18 and 60.