Ashtanga yoga practitioners should take rest on the days of the new or full moon. This is in addition to the regular rest day during the week.

Why?

The sun and the moon both exert gravitational pulls on the earth, and their relative positions create energy differentials. These pulls affect both our mind, and our body.

It can make us feel light and airy (energetic but ungrounded) or heavy and stiff (grounded but lethargic). This creates an issue for practicing yoga because you need both energy, and to be well grounded if you want to progress safely through the serie(s).

That said – you may not “feel” the affects of gravity in your everyday life. With everything we have going on, it’s tough to be that “in tune” with nature.

Here is also another explanation by Eddie Stern, a highly respectful and senior teacher in Ashtanga community, you can read here.