The Astronomical New Moon, or the invisible New Moon, is the moment when the moon is almost directly between the earth and the sun. At this moment the moon's dark surface faces the earth. Therefore it is completely invisible even if it occurs in the middle of the night. The date and time of this invisible New Moon is commonly found in almanacs, newspapers and calendars. Return to Top of the Page.
Elongation is the angular distance between the moon and the sun.
With passage of time the moon in its circular motion around the earth, moves away from the alignment with the earth and the sun. The angular distance between the moon and the sun increases, and some 18 to 24 hours after the Astronomical New Moon, the moon will have moved sufficiently for the sunlight reflected off its outer edge to be directed towards earth. The new crescent moon can now become visible on earth. Elongation is a critical factor in determining the crescent's visibility, and this depends on more than just time. No sighting can penetrate this barrier, which is set by shadows cast by the rough lunar terrain.