The Solar is considered to be an outward shining energy, and the Lunar to turn inward reflectively.
In advanced yogic breath training, these are the two "Nadis" or energy channels that run along side the spine and terminate in your two nostrils.
In many traditions, you hear of eclipses as a time when misfortune is readily available and one should exercise extreme caution. We can imagine how this thinking likely comes down from our early human ancestors - think of how the sky going dark in the middle of the day would affect people's psyches in ancient times!
There's a more subtle reasoning in the traditions though - and it has to do with these internal channels:
In some schools of thought, the solar and lunar energies can both be powerful, but neither is particularly centered - they each lean too far to the right or left. Too much solar current and you find yourself blaming everyone else, too much lunar and you turn that blame inward on yourself. Too much sun and you're always seeking outside yourself for peace, too much lunar and you're withdrawing too much. The goal of the Hatha yoga traditions is to find the nondual union or stillpoint between these two polarities of our being.
Because of this, students were advised to reduce their activities and engage in spiritual practice during the time of an eclipse - to counterbalance what are considered to be inauspicious circumstances.
with training this balance of the Solar and Lunar energies in one's being is said to facilitate moving into the realization of nondual stillness. Because the energies are thought to equalize as the sun and moon conjoin, it is felt that an advanced practitioner can use that outer conjunction to find a third way within, which harmonizes and subsumes duality. This third way is the central channel - the Sushumna Nadi, toward which all hatha yoga practice is aimed.
I hope you've enjoyed learning about these mystic and alchemical worldviews of harmonizing the inner body with the outer world. In some parts of the Northern Hemisphere you may have the opportunity to view a solar eclipse tomorrow morning, anywhere nearby, say the mystics, you can benefit from these rare and unique "energies". Try some of these practices out and see how they work for you!
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