When the moon has completed the first quarter of a revolution it is ninety degrees east of the sun and presents the phase known as "half-moon" since half of the surface that is turned toward the earth is illuminated and half is in darkness. It is said to be "at the first quarter." The illuminated half is of course the western half because the sun is to the west of the moon. The half moon is near the meridian at sunset and sets near midnight. Up to the first quarter, then, the moon is a crescent in the western sky during the first part of the night and should never be represented as east of the meridian or near the meridian at midnight.