what is the shape of a crescent moon
Crescent The crescent shape consists of a circular disk with a segment of another circle removed from its edge, so that what remains is a shape enclosed by two circular arcs of different diameters which intersect at two points (usually in such a manner that the enclosed shape does not include the center of the original circle). As such, it belongs to the class of figures known as lune in planar geometry. The tapering towards the points of intersection of the two arcs are known as the "horns" of the crescent. The classical crescent shape has its horns pointing upward (and is often worn as horns when worn as a crown or diadem, e.g. in depictions of the lunar goddess, or in the headdress of Persian kings, etc.[7]
Umbra, penumbra and antumbra The umbra (Latin for "shadow") is the innermost and darkest part of a shadow, where the light source is completely blocked by the occluding body. An observer in the umbra experiences a total eclipse. The umbra of a round body occluding a round light source forms a right circular cone; to a viewer at the cone's apex, the two bodies are equal in apparent size. The distance from the Moon to the apex of its umbra is roughly equal to that between the Moon and Earth (384,402 km (238,856 mi)). Since Earth's diameter is 3.70 times the Moon's, its umbra extends correspondingly farther: roughly 1,400,000 km (870,000 mi).[1]