The Christian calendar is packed full of days of observance, religious festivals and Holy Days, from All Saints' Day to Candlemas to the Feast of the Transfiguration. Among the most popular, though, is Pancake Day, which this year falls today, February 9.

Many of us will know that this means Lent is upon us, but we might be a bit hazy on the details. Here's everything you need to know.

When does Lent start? It falls differently every year according to the Liturgical calendar, but this year begins tomorrow, February 10, known as 'Ash Wednesday'. The Lenten season ends on Holy Saturday, the day before Easter Sunday, which this year falls on March 26.

What's Shrove Tuesday all about, then? 'Shrove Tuesday', or Pancake Day as it is perhaps better known in the Western world, is the last day before Lent begins. 'Shrove' comes from the word 'shrive', meaning to confess and receive absolution, and indicates a period of cleansing, where an individual abstains from certain things as a way to draw closer to God.

Traditionally it was a day of repentance, but many Christians now use Shrove Tuesday to indulge in foods that they plan on fasting from over the next few weeks. During the Middle Ages, families tried to use up all their rich foods, like milk, fats, eggs and sugar ahead of the Lent period, hence the practice of eating pancakes. In France, the day became known as 'Mardi Gras', or 'Fat Tuesday', partly due to the consumption of these fatty foods.

What actually happens during Lent? Symbolic of the 40 days Jesus spent fasting in the wilderness, resisting the Devil's temptations and preparing for his ministry, many Christians choose to fast from indulgences such as sweets, chocolate, coffee, alcohol, or even TV during Lent.

The eagle-eyed among you will notice there are more than 40 days between Ash Wednesday and Holy Saturday – 46, to be precise. This is because Sundays don't count; each represent a kind of 'mini-Easter', and are considered a feast day to celebrate the resurrection.

So what should I give up? This one's totally up to you – it's not obligatory, though many Christians find Lent a great time to reset, and use the period of fasting to give up things which may have got in the way of their relationship with God. Others choose to pick up something, like doing an act of kindness every day, or committing to reading the whole of the New Testament before Easter.

Environmental activist Ruth Valerio has made another suggestion for a Lent challenge. Watch the video below to find out more: