A planet too close to the Sun is called combust, and its effects are said to be burnt away. For the Moon, that condition is simply the new moon.

Traditional limits put combustion within about 8°30' of the Sun and 'under the beams' within 17°, which for the Moon means the two or three days either side of new. It is one of the places where astrological doctrine and plain observation agree exactly: those are the days you cannot see it.