circle of fifths

[nils152]

What exactly is the circle of fifths?

[Dommy]

C G D A E B F# C# G# D# A# F C

or

C G D A E B Gb Db Ab Eb Bb F C

It's also the circle of fourth backwards.

C F Bb Eb Ab Db Gb B E A D G

It takes turns of the cycle to return back to "home."

[nils152]

but what are these used for?

[zog]

The circle of fifths is a visual aid that shows you the relationship between keys. If you start at the top with C and go clockwise around the circle the number of sharps increase by one with each letter. For example C has no sharps or flats in that key G has one sharp D has two sharps and so on. If you go counter clockwise you add flats instead of sharps.