詳しいガイド（英語）
Meaning and tradition
Akasha is Sanskrit for space or ether, the subtlest of the five elements in Indian philosophy, and the gesture is also called the Mudra of Space or Ether Mudra. It belongs to the hasta mudra systems popularized in modern yoga and Ayurveda-influenced hand-gesture manuals, and is not a gesture from the classical hatha yoga texts. The spelling Akash reflects the common Hindi form.
By the finger map, thumb is fire, index is air, middle is space, ring is earth, little is water. Joining the middle finger (space) to the thumb (fire) is read in these systems as strengthening the space element.
How to practice
Sit in Easy Pose or Lotus Pose with the spine long. Rest the hands palm up on the thighs or knees. Touch the middle fingertip to the thumb tip; the other three fingers stay straight but soft.
Om Breath is the classic pairing, with a long, even chant on the exhale. Bhramari Breath, the humming bee breath, also works. Hold for 10 to 20 minutes, then release.
Settle first, then form the gesture. Spend a few breaths noticing the weight of the body on the seat, and only then bring the finger and thumb together. If the hands feel stiff, rub them together for a moment beforehand so the fingers move easily. A cushion under the hips usually makes a long hold far more comfortable than any adjustment of the fingers.
Tips and common mistakes
Keep the contact light; pressing tightens the forearm.
Mind which fingertip touches. Unlike Gyan Mudra, where the index touches the thumb, here it is the middle finger and the index stays extended. Unlike Prithvi Mudra, where the ring finger touches, here the ring finger stays extended. Unlike Shunya Mudra, where the middle finger is folded to the thumb base and covered by the thumb, here the middle fingertip meets the thumb tip and nothing is folded.
The middle finger is long, so avoid tipping the wrist to reach; keep the wrist neutral.
Keep both hands identical and the palms up.
Tradition vs. evidence
Claims that this gesture treats ear problems or sharpens hearing are traditional and unsupported by clinical research. What is defensible is the simple hand shape as an attention anchor and its pairing with chanting or humming, whose calming effect comes largely from slow, extended exhalation.