(CNN)Yom Kippur, or the Day of Atonement, is the holiest day of the year in Judaism.
When is it: It falls on the 10th day of the Jewish month of Tishrei. Because the Jewish calendar is lunar, the holiday begins this year at sundown on Tuesday and ends at nightfall on Wednesday.
What it observes: It's a chance to wipe one's slates clean of the wrongs committed over the past year.
How it's practiced: It's a day of fasting, repentance and worship. In addition to refraining from eating and drinking, observant Jews do not bathe on the holiday, they do not wear leather shoes or gold jewelry, and they do not engage in spousal intimacy.
Services during Yom Kippur are held continuously through the day and include readings from the Torah and the reciting of prayers expressing regret or asking for forgiveness.
Yom Kippur services conclude with closing prayers and the blowing of the shofar, a ritual musical instrument carved from the horn of a ram.
How it began: According to Jewish tradition, the origins of Yom Kippur date back to the time of Moses, after the people of Israel made their exodus from Egypt. When they arrived at Mount Sinai, Moses was given the Ten Commandments by God. When Moses came down the mountain, he found the people worshiping a golden calf. Moses destroyed the tablets in anger, but the people atoned for their sin, so God forgave them.