In Sanskrit, Surya refers both to the physical sun and to the sun-god, and is one of the most important symbols in their cosmology. The Upanishads refer to the physical sun as agni. As in Western occultism (for example the Tarot and astrology), for Hindus the sun signifies life, success, energy, honor, the father, respect and power, and rules the astrological sign of Leo. However, the term Surya is also used in esoteric Yoga and spirituality to indicate the light of inner illumination and truth, or the dawning of realization. Thus one of the most important forms in Hatha Yoga is Surya Namaskar, or the sun salutation, which a Yoga practitioner tries to perform each day at dawn facing the rising sun, and which involves a series of stretches and prostrations. It is believed that besides the physical benefits of stretching, the spiritual attitude created by prostrating to the sun each day is good for both health and spiritual well-being.

In ancient times, when the Vedas were written, Surya was one of the three most important Hindu gods; however, in later times Surya became a more mythical god, replaced in religious importance by Vishnu, and especially Vishnu's greatest avatar, Krishna. However, Surya remains very important in Hindu ritual, especially in the Gayatri mantra, and millions of people till worship and pray to the sun god every day, especially prayers for health and fertility. He is said to reside in Suryaloka (which means, unsurprisingly, the Abode of the Sun), and to have had two wives, Sanjana and Chaya, and several children, including Yama, the lord of death, a very important figure in the Upanishads in his own right. In fact, Hindu kings frequently traced their lineage back to the actual person of Surya, who is said to have begun the line of Vedic rulers, of which Rama was the 66th. His iconography has become extremely complex over the millennia of his worship, but some of the most important symbols are his solar chariot, driven by the charioteer Aruna who shelters the world from the worst of his brilliance, and pulled by seven horses representing the days of the week; knee-length boots and metal gloves; and an erect, immobile posture which is supposed to represent perfection and strength.


A great deal of further information can be found here:
http://webonautics.com/mythology/surya.html
http://www.indiayogi.com/website/phase2/indiangods/surya.asp