A D major scale employs F-sharp and C-sharp, while a G major scale employs F-sharp.  The consistent employment of sharp(s) or flat(s) in the scale becomes a musical notation called key signature, designating notes that are to be played with sharps or flats throughout the piece unless altered by an accidental.

3. Circle of Fifths

A D major scale employs F-sharp and C-sharp in the key signature while a G major scale employs F-sharp only. Why is that? The circle of fifths is a geometrical representation of relationships covering all 12 pitches in music. You will see the operation starting from the apex and proceeding clockwise by ascending fifths, so a G major has one sharp, a D major has two sharps, and so on adding a sharp each time. Similarly, it proceeds counterclockwise from the apex by descending fifths, so an F major has one flat, a B-flat major has two flats, and so on. At the bottom of the circle, the sharp and flat keys overlap, showing enharmonic key signatures.

Click to see and learn more about the circle of fifths!

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