where each tick mark represents a semitone. Scales and modes The pitch constellation provides an easy way to identify certain patterns and similarities between harmonic structures. For example. A major scale consists of a circle with markings at 0 (or 12), 2, 4, 5, 7, 9 and 11 o'clock. A minor scale consists of a circle with markings at 0 (or 12), 2, 3, 5, 7, 8 and 10 o'clock. The diagrams above show the two scales marked with "scale degrees". It can be observed that the tonic, second, fourth and fifth are shared, while the minor scale flattens the third, sixth and seventh notes relative to the major scale. Another observation is that the minor scale's constellation is the same as the major scale, but rotated +90 degrees. In the following drawing all of the major/minor scales are drawn. Note that the constellation for all the major scales or all the minor scales are identical. The different scales are generated by rotating the note overlay. The notes that need to be sharpened/flattened can be easily identified. Moreover, if we draw all seven diatonic modes we can see them all as rotations of the Ionian mode. Note also the significance of the 6 o'clock point. This corresponds to a tritone. The modes including pitches a tritone from the tonic (Locrian and Lydian) are least used. The 5 o'clock and 7 o'clock pitches are also important points corresponding to a perfect fourth and perfect fifth respectively. The most used scales/modes - major (Ionian mode), minor (Aeolian mode) and Mixolydian - include these pitches. Symmetric scales have simple representations in this scheme. More exotic scales - such as the pentatonic, blues and octatonic - can also be drawn and related to the common scales. A more complete list of musical scales and modes Other overlays In previous sections we saw how various overlays (scale degrees, semi-tone numbering, notes) can be used to notate the circumference of the constellation. Various other overlays can be laid around the constellation. For example: Intervals. Solfège. Pitch ratios (ratios of pitch frequencies). Note that once a pitch constellation has been determined, any number of overlays (notes, solfège, intervals, etc.) may be placed on top for analysis/comparison. Often generating one harmonic relationship from another is simply a matter of rotating the overlay or constellation or shifting one or two pitch locations. Chords Similarities between chords can also be