Surya Namaskara

Even if you are not practicing an Ashtanga sequence, most yoga classes generally start with Sun Salutations.  There are some obvious reasons why one would what to start a class with this flow sequence.  It limbers and warms the whole body in preparation for the rest of your yoga practice.  It also guides the mind in to concentration on the practice.
Historically, the origins of the Sun Salutations lies in the worship fo the Hindu God of the Sun and God of health, Surya.  and the tradition begin to practice this sequence at or around sunrise as this represented the awakening of Surya and was considered the most spiritually favorable time of the day.
Sri K. Pattabhi Jois said, “”… let me repeat that no asana practice is complete without sun worship. Without its focusing of mental energies, yoga practice amounts to little more than gymnastics and, as such, loses meaning and proves fruitless. Indeed the Surya Namaskara should never be mistaken for mere physical excersize –for something incidental, that is, that simply precedes the asanas of yoga. Therefore, it is necessary, before beginning the sun salutations, to pray to Surya […] to bestow upon us the good fortune of having only good thoughts, of hearing and speaking only good words, and of attaining a sound and strong body, so that we may have a long life and, one day, achieve oneness with God.”
It is hard to determine the origin of the actual sequence.  Some Yogis maintain that the sequence itself is 2,500 years old while others believe it to be created as recently as the 1920’s of the 1930’s.
Regardless of the origins, the physical wholeness of the routine and the ability to have it calm the body when completed slowly or invigorate the body when completed at a faster pace, it is certainly a nice way to start the day.