Moon Days
“That day is very difficult day. Two stars one place(conjunction) is going. New moon also, full moon also. That day very dangerous day. You (take) practice (on that day), anyone can have a small pain starting. That pain is not going very quickly. Long time he is taking. Some broken possible. That is why that day don’t do.”

Like all things of a watery nature (human beings are about 70% water), we are affected by the phases of the moon. The phases of the moon are determined by the moon’s relative position to the sun. Full moons occur when they are in opposition and new moons when they are in conjunction. Both sun and moon exert a gravitational pull on the earth. Their relative positions create different energetic experiences that can be compared to the breath cycle. The full moon energy corresponds to the end of inhalation when the force of prana is greatest. This is an expansive, upward moving force that makes us feel energetic and emotional, but not well grounded. The Upanishads state that the main prana lives in the head. During the full moon we tend to be more headstrong.

The new moon energy corresponds to the end of exhalation when the force of apana is greatest. Apana is a contracting, downward moving force that makes us feel calm and grounded, but dense and disinclined towards physical exertion.

The Farmers Almanac recommends planting seeds at the new moon when the rooting force is strongest and transplanting at the full moon when the flowering force is strongest.

Practicing Ashtanga Yoga over time makes us more attuned to natural cycles. Observing moon days is one way to recognize and honor the rhythms of nature so we can live in greater harmony with it.


“Why is it said that the practice of yoga shouldn’t be done on certain days. For example the new and the full moons?
Let me explain. The shastras (sacred books) have marked certain days as days on which no study, or adhyana (meditation), should be done. It is also understood that the moon has a great impact on human thought. For example on the new-moon day the light of the moon would be in a completely diminished state, thereby diminishing the power of your own mind to reflect good and powerful thoughts. Also, on a full-moon day, when the moon is shining at his brightest, a situation or scenario exists where there could be a state of severe agitation of the mind, which again is not conductive for any kind of meditative or contemplative activity, like yoga. Any planetary extremity should be taken note of and acted upon so that the pursuit of an intellectual practice is not affected.

Does the knowledge of a teacher who teaches on these two days decrease ?
Indeed, there is a Sanskrit shloka (verse) that hints at the teacher being affected as well as the students being subjected to a sense of ill will. The intellectual growth of the shishya (disciple) could become stunted if he were to take lessons on these two days. His mind could become dull and unresponsive. Even while we were students at the Sanskrit College, these two days, and also the first three days after, were considered unsuitable for any form of serious study. These things have been concluded in the shastras since time immemorial. It is not for us to ask why but just to follow. We all have been following the same lineage laid down by the rishis (seer, sage) of the past. The dharma shastras are the cornerstone around which is built everything in our culture. Adherence to the shastra will lead to peace and prosperity, the flouting of (the shastra) would result in chaos…”
We, as ashtanga yoga practitioners, don’t practice during the moon days because they are said to be the “yoga holidays” in the ashtanga yoga tradition. 
Moon days are the new and full moon days.
 Here is an explanation of why we don’t practice during the moon days by Guruji, Sri K Pattabhi Jois;
It is not only the yoga practice that we don’t do but all other mental activities are being affected by the moon during those days according to T.S. Krishnamurti, a renowed astrologer and a student and a lifelong friend of our Guruji. 
Here is the interview with Krishnamurti from the Book Guruji: The portrait of Sri K. Pattabhi Jois Through the Eyes of His Students.