Full Moon Meditation
The sun is the source of life and consciousness, while the moon is like the mind: reflective and mutable. Like the sun, the Self, or consciousness is effulgent (radiant), while the moon and the mind reflect that light.
While the sun always appears one and the same, the moon goes through phases and appears differently at different times. In the same way, consciousness is ever one and the same, while the mind goes through continuous mutations.
Due to its ever changing nature, the mind is also likened to water, or mercury, ever moving and changing, until it finds its rest. But when these mental fluctuations subside, the mind becomes perfectly reflective like a mirror, like the full moon, like a crystal clear lake:
kṣīṇa-vṛtter abhijātasyeva maṇer grahītṛ-grahaṇa-grāhyeṣu tat-stha-tad-añjanatā samāpattiḥ - YS 1.41
“when the mental fluctuations have been eliminated, the mind becomes perfectly transparent, like a gem stone - whatever is placed next to it is represented perfectly in the mind - whether that be an object reflected on (in meditation), the mind that reflects, or the ego (cognizer) that is associated with the mind.”
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Sunset Yoga and Meditation