Surya, sun, plays an important role in Yogic practices. In Hatha Yoga, the sun is said to be situated in the human body at the navel (nabhi).
Ancient Hindu thought seems to be highly influenced by the energy giving and life sustaining aspects of the Sun. We find the Vedic seers praying to the Sun God by way of the famous Gayatri Mantra, meditating upon the Sun’s deeper radiant nature and expressly desiring to receive enlightenment from it (Yajur Veda 36.3).
In Hatha Yoga, the sun is said to be situated in the human body at the navel (nabhi). It presents heat, energy and the fire that digests the food we eat. It is said that the Sun devours the elixir secreted by the moon, which is located inside the skull at the base of the palate (talumula) and that due to this human beings suffer from old age and death (Hatha Pradipika III.7; Gheranda Samhita: III.28). To stop this processo deterioration a technique of inverted position (viparita karani) is recommended in hatha yoga.
It is found that breathing in (puraka) through the right nostril increases heat in the body. Hence the right nostril is called Surya nadi and the left nostril is called Chandra nadi.
In Yoga Kundalini Upanishad (I.22-25) the technique of Surya Kumbhaka or Surya Bheda pranayama is mentioned. It involves breathing in (puraka) through the right nostril, followed by holding the breath (kumbhaka) and then breathing out (recaka) through the left nostril.
Suryabhedana, as one of the eight varieties of pranayama, is described in the same manner in various Yoga texts. In Hatha Yoga Pradipika (II.50) it is said to clean the skull (kapala sodhanam), remove impurities arising from excess of wind (vata dosha), and get rid of worms from the intestines.