The International Day of Yoga is celebrated annually on 21st June since its inception in 2015. June 21st is the longest day of the year in the Northern Hemisphere and shares special significance in many parts of the world. From the perspective of yoga, the summer solstice marks the transition to Dakshinayana. The first full moon after summer solstice is known as Guru Purnima. Shiva, the first yogi (Adi Yogi), is said to have begun imparting the knowledge of yoga to the rest of mankind on this day, and became the first guru (Adi Guru). Dakshinayana is also considered a time when there is natural support for those pursuing spiritual practices.