Ekadashi (एकादशी) is the eleventh lunar day (tithi) of the waxing (Shukla Pakṣa) and waning (Kṛṣṇa Pakṣa) lunar cycles in a Vedic calendar month. Ekadashi is popularly observed within Vaishnavism, a major denomination within Hinduism. Followers offer their worship to the god Vishnu by fasting.
Within Hinduism, the primary purpose of fasting on ekadashi is to gain control over the mind and bodily senses, and channel it towards spiritual progression. In addition, there are several health benefits linked to fasting. High protein and carbohydrate-containing foods such as beans and grains are not consumed. Instead, only fruit, vegetables, and milk products are eaten. This period of abstinence starts from sunrise on the day of ekadashi to sunrise on the following day. Rice is not eaten on ekadashi.
The timing of each ekadashi is according to the position of the moon. The Indian calendar marks progression from a full moon to a new moon as divided into fifteen equal arcs. Each arc measures one lunar day, called a tithi. The time it takes the moon to traverse a particular distance is the length of that lunar day. Ekadashi refers to the 11th tithi, or lunar day. The eleventh tithi 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 ekadashi, and in the dark half of the lunar month, the moon will be about 3/4 dark on ekadashi.
There are usually 24 ekadashis in a calendar year. Occasionally, there are two extra ekadashis that happen in a leap year. Each ekadashi day is purported to have particular benefits that are attained by the performance of specific activities.
Bhagavata Purana (skandha IX, adhyaay 4) notes the observation of ekadashi by Ambarisha, a devotee of Vishnu.
The story behind ekadashi began with Vishnu sleeping or in a meditative state. A demon, Murdanav, approaches and attempts to attack Vishnu. At that time, a beautiful woman sprung forth from Vishnu's 11th sense (often called the "mind").