Yoga is a physical, mental, and spiritual practice or discipline that originated in India. The Indian Prime Minister Narendra Modi in his UN Address suggested the date of June 21, as it 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 Poornima. 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.
This video is a film by RGUKT-Nuzvid YOGASALA to commemorate the International Yoga Day.