Traditionally the summer solstice (June 21) is celebrated by the performance of 108 sun salutations (Surya Namaskara) with the number 108 being significant for a number of reasons which I will be expounding upon in another post.
This film does a great job of introducing one to the rich history of yoga and is very appropriate for today as is mentioned in the film, in 2014 the Prime Minister of India proposed an International Day of Yoga to the United Nations. 177 Nations co-sponsored the resolution (a record in UN history) and today, the 21st of June, was chosen.
Namaste
-Brian