One astronomical term which is rarely used anymore is “combust,” which refers to a celestial body that appears to be in such close proximity to the sun that it is impossible to observe. 

The moon is a very good example of this from roughly 18 to 24 hours before to roughly 18 to 24 hours after new moon phase. Of course, when the moon is new, we are facing that part of the moon that is not illuminated by reflected sunlight. But even when a narrow sliver of the moon’s disk is illuminated, shortly before or after new, it may still be difficult, if not impossible, to see.