Surya Namaskar (सूर्य नमस्कार )

Surya namaskar (Sun Salutation) is a practice of Hath yoga which is regarded as an essential aspect of asana practice. Even though it was not the part of traditional hatha yoga, it was later incorporated as a important aspect of asana practice. Surya namaskar is a sequence of asana which is practiced in a continuous and repetitive manner for certain rounds in both sides of the body. Traditionally it has twelve steps which are combination of twelve asanas. However, it can be practiced with some modification to intensify the practice while not delineating from the core aspect of Surya Namaskar (Sun Salutation).
Surya namaskaar is generally translated as sun salutation based on the idea that the sun ,symbolizes spiritual consciousness, represents pingala nadi which carries the vital, life-giving force.
Surya namaskar(Sun Salutation) is considered a complete sadhana because of the inclusion of asana(posture), pranayama, mantra and meditation techniques. This practice helps to energize the solar energy of body which flows through pingala nadi which leads in balancing energy system mentally and physically.
Surya namaskar(Sun Salutation) stimulates and balances all the systems of the body such as reproductive, circulatory, respiratory, digestive systems. Modified version of Surya Namaskar has been practiced merely for practice purpose. The Surya Namaskar In Hatha Yoga (Modified) is not performed to divert and demote the sacred practice of traditonal Surya Namaskar. The modified version can also be practiced just for the shake of practice. 

There are 12 steps in traditional Surya Namaskar (Sun Salutation) . Among those 6 asanas are practiced twice to make it 12 step. The following are the 12 step of asana that are included in Surya Namaskar:

1.  Pranamasana (Prayer Pose)
2. Hasta Utthanasana ( Raised Arms Pose)
3. Padahastasana ( Hand to Foot Pose)
4.  Ashwa Sanchalanasana (Equestrian Pose)
5.  Parvatasana (Mountain Pose)
6.  Ashtanga Namaskar (Salutation with Eight Limbs Pose)
7.  Bhujangasana ( Cobra Pose)
8.  Parvatasana ( Mountain Pose)
9.  Ashwa Sanchalanasana (Equestrian Pose)
10. Padahastasana (Hand to Foot Pose)
11. Hasta Utthanasana ( Raised Arms Pose)
12.  Pranamasana (Prayer Pose)

Completion of the 12 step, it becomes one half round of Surya Namaskar (Sun Salutation). The first round is started from the right side followed by the left which moves in alternative manner. Along with the start of each side, a mantra is chanted.Following are the mantras dedicated to God Surya(Sun).

1.   Om Mitraya Namaha (Salutation to the friend of all)
2. Om Ravaye Namaha ( Salutation to the Shining One)
3. Om Surya Namaha (Salutation to one who induces activity)
4. Om Bhanave Namaha (Salutation to one who illumines) 
5. Om Khagaya Namaha (Salutation to one who moves quickly in the sky)
6. Om Pushne Namaha(Salutation to the strength giver )
7. Om Hiranya Garbhaya Namaha ( Salutation to the golden, cosmic self)
8. Om Marichaye Namaha (Salutation to the Lord of the Dawn)
9. Om Adityaya Namaha ( Salutation to the son of Aditi, Cosmic Mother)
10. Om Savitre Namaha (Salutation to the Lord of Creation)
11. Om Arkaya Namaha (Salutation to one who is fit to be praised)
12. Om Bhaskaraya Namaha (Salutation to one who leads to enlightenment) 

There are 6 bija mantras as well which are repeated four times during a one round which includes right and left side. They are as follows:

1. Om Hraam
2. Om Hreem
3. Om Hroom
4. Om Hraim
5. Om Hraum
6. Om Hrah

Practice time: It is ideal to practice at sunrise and sunset. It can be practiced any time if the stomach is empty. Surya Namaskar (Sun Salutation) can be practiced 3 to 12 rounds as per the traditional yogic book recommend. The speed of the Surya Namaskar (Sun Salutation) can be be faster if it is practiced for exercise purpose. It can be medium it is is done for spiritual sense and can be practiced slower if is done for therapeutic benefits. For cleansing the body, it can be done up to 108 times which can be strenuous and heavy practice for many. That's why it is recommended to increase the number with plus one system.
Precaution: In case of fever, acute inflammation, boils or rashes because of excess toxins in the body, it is advised to discontinue the practice.
During menstruation period, it is advised not to practice.

Source: (Asana Pranayama Mudra Bandha)