This Viparita Karani word means Sanskrit inverted. One has to lie down relaxed. Gradually raise both the legs and the hips. Support the waist with hands more or less in Sarvanga Asan pose.
By this practice, the positions of the Sun and Moon are reversed. Hence, it is called Viparita Karani.
It is the opinion of yoga masters that the sun dwells in the navel and moon in Sahasrara. The nectar that flows from the moon is consumed by the fire at the navel. This leads to decay and death. But by the constant practice of this mudra the nectar of the moon is preserved.
Duration recommended is a few minutes to start with but can be gradually increased to two hours or more. After a few weeks, the face shines with spiritual lustre, wrinkles are removed, eyes become healthier, and digestion becomes keen.