"Standing straight on the left leg, bend the right leg and place the right foot on the root of the left thigh. Stand thus like a tree on the ground. This is called vriksha-asana." Gheranda-samhita II.36
The Half Moon Pose (Ardha-chandra-asana) Instruction:
1
Stand in the tada-asana (Stand with both feet touching from the heel to the big toe, keeping the back straight and the arms pressed slightly against the sides with palms facing inward.
2
Bring the hands together at the chest with palms lightly pressed against each other (the Anjali-mudra).
3
Inhale and raise the arms straight up keeping the palms pressed lightly together.
4
Arch your body backwards keeping your arms alongside your neck and head, tilt the head backward and hold. Keep your knees straight while holding posture.
5
Slowly return to the tada-asana.
Comments:
The ardha-chandra-asana is a basic stretching and balancing pose that benefits principly the lower back, abdomen and chest. It is equally suitable for use in your stretching routine as well as formal asana practice.
This pose is also one the postures that are are sequenced in surya-namaskar (the Sun Salutation).
The Yoga Sutras
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