The Circle of Fifths
The Circle of Fifths is a common music theory tool used to show the relationship of all the tones of the chromatic scale. The Circle of Fifths starts at the top with the Key of C Major. C Major is the natural scale meaning it has no sharp or flat notes in its scale. Moving clockwise the next Key is G, which is the fifth of C (C D E F G). Each key after C adds a sharp as the Circle of Fifths continues. The key of G has one sharp note, the next fifth, D, has two sharp notes, and so on (shown by the black #, or sharp symbols next to each key).
Reading the Circle of Fifths counterclockwise shows the keys that contain flat notes, the key of F having one flat note in its scale, Bb having two flat notes and so on (shown by the black b, or flat symbols next to each key).