A person can draw a simple moon using a circle or crescent shape, with or without the facial features of a cartoon moon. To draw a detailed, realistic moon, a person could use shading to indicate the darker areas and ensure accurate placement and shape by referring to moon photos.
When drawing the moon, it is the "maria" whose shapes and shading makes a drawing recognizably a moon. Maria is the Latin word for "seas," and they are the dark splotches on the moon. They are low-lying areas filled with dark, ancient, hardened lava from when the moon was volcanically active. A singular sea is called a "mare."
The largest maria visible to the naked eye are Mare Imbrium, Mare Serenitatis, Mare Tranquillitatis, Mare Nubium and Mare Fecunditatis. Especially towards the top half of the moon, some of these maria appear to run together, which makes drawing their equivalent shapes a little easier. Mare Crisium is small but very clearly separate from other maria so it's a good recognizable mare to include in your drawing. Referring to the actual moon, or a photo or previous drawing of the moon can assist a person in reproducing the maria's shapes.
Although the highlands of the moon look white in comparison to the maria, some brightest white highlights on the moon are actually the largest craters. Copernicus, Tycho and Langrenus are the major white spots on the moon people can see from earth. If the maria are darkly shaded and the highlands are lightly shaded, the craters can be left completely white to create an accurate drawing of the moon.
To draw a perfect circle, an artist can use a compass or trace around something that is already circular like a coin or the base of a cup or plate. To draw a crescent moon, an artist can use one of those same tools but stop his arc halfway, and freehand the rest of the crescent.