circle of 9's, what is the format?

Question

they are 12 musical scales. there is a format to remember it and learn them. i think it it was called "circle of 9's" the 9 meaning the possibilty of flats and sharps. i did know it at one time in high school but cannot remember it. please help.

Answer 1

It's circle of fifths. It starts out:
C major: No sharps
G major: one sharp
D major: two sharps
etc.

Going the other direction, you get:
Cmajor: no flats
F major: one flat
B flat major: two flats
etc.

Answer 2

your other direction is a circle of fourths