Ekadashi, also spelled as Ekadasi, is an auspicious day which occurs twice in a Hindu calendar month. It is the eleventh lunar day (tithi) of each of the two lunar phase which occur in a Hindu calendar month – the Shukla Paksha (period of the brightening moon also known as waxing phase) and the Krishna Paksha (period of the fading moon also known as waning phase).
In Hinduism it is considered a spiritually beneficial day and is usually observed by a partial fast. Beans and grains are not eaten during Ekādaśī, as on this day these two foods are believed to be contaminated by sin. Only fruits, vegetables and milk products are eaten during Ekādaśī. This period of abstention runs from sunrise on the day of Ekādaśī to sunrise on the day following Ekādaśī.
Two Ekādaśīs occur in one month according to positions of the moon. The progression of the moon from full moon to new moon is divided into fifteen equal arcs. Each arc measures one lunar day, called tithi: The time it takes the moon to traverse that distance is the length of that lunar day. Ekādaśī refers to the 11 tithi, or lunar day. The eleventh tithi therefore corresponds to a precise phase of the waxing and waning moon: In the bright half of the lunar month, the moon will appear roughly 3/4 full on Ekādaśī, and in the dark half of the lunar month, the moon will be about 3/4 dark on Ekādaśī.