About Moon Days
Why We Don’t Practice on Moon Days
It has always been the tradition in Ashtanga Yoga to rest from asana practice on new and full moon days (tithis). When asked why we shouldn’t practice on these days, Guruji was fond of saying, “Two ‘planets’ [grahas] one place, very dangerous.” What is meant is that on these days, the sun and moon are in a line relative to the position of the earth. Consequently, the gravitational forces are combined, and the effect of these ‘planets’ more pronounced. One definitive effect is that the ocean’s tides are higher and lower on these days. When āsana practice is done daily, rest days are important for regeneration; and the extra biweekly ‘moon day’ comes as a welcomed respite.
Why do Jois Moon Days Sometimes Seem a Day Early?
We use an Indian astrology system of calculation (rather than a simple astronomy calculation). In this system, the period of time prior to the point the moon becomes exactly new/full is considered as the ‘moon day’ (called a tithi in Indian Astrology). Further more, the day is considered to begin at sunrise rather than mid-night. (for example, if the moon is exactly full on a Tuesday at 3am, Monday is called as the moon-day. If it becomes full after the sun rises on Tuesday then Tuesday is called the moon-day).
Our moon days come from the following online source: www.mypanchang.com ».
Further explanation: In India, where yoga comes from, the term ‘moon day’ is a loose translation of the Sanskrit term ‘tithi,’ and would be more accurately translated as ‘lunar phase’ rather than ‘moon day.’ Each tithi is the time period that it takes for the the moon to traverse 12° in the sky. Thus there are 30 tithis (or lunar phases) in one complete lunar cycle. Due in part to the elliptical path of the moons orbit, the length of each tithi varies significantly and begins at varying times of day. Tithis vary in duration from approximately 19 to 26 hours. What loosely gets termed the full and new ‘moon days’ are actually the 15th and the 30th tithis of this Indian Astrology (Jyotish) system.