cool huh ?
:D in the next key, a perfect fifth away, only one note of the seven is different..
thats why these keys are the closest neighbours.
if we examine the key sig of C to start with, no sharps or flats..
a 5 in one direction we have G, one sharp..
in the other diection, F - one flat..
so it follows the key sig with 2 sharps, is D, with 3, A etc etc etc..
and in the other direction the flats... 2 put u in Bb, 3 in Eb etc..
the two major modes other than ionian that u know are a perfect fifth away in either direction, so only one note different in both cases from the 'do,re, mi, fa, etc ionian..
btw.. haha just to confuse you further, a perfect fifth if counted in the other direction is a fourth, or what interval guitar stirngs (mostly) are tuned to..
Aaaahhhhhhhhhh not the circle of fifths. I really think this was the only part of music thereoy that one of my professors knew. That's all she would teach...without teaching us how to actually apply it to our own music.