The Lydian and Mixolydian modes
Build two major-sounding modes and name the single degree that sets each apart from major.
The Lydian mode
The Lydian mode is major with a raised fourth degree. From the tonic to the fourth is a tritone, and the mode sounds "floating", a little magical: film composers love it.
On the white keys Lydian starts on F. From another note: take major and raise the fourth. C Lydian is C major with F♯.
F Lydian: the white keys from F
C Lydian: C major with F♯
Practice: Name the mode (1)
Practice: The difference from major
The Mixolydian mode
The Mixolydian mode is major with a lowered seventh degree. There is no leading note, and the mode sounds plain and open: it is common in rock, folk and traditional music.
On the white keys Mixolydian starts on G. From another note: take major and lower the seventh. C Mixolydian is C major with B♭.
G Mixolydian: the white keys from G
C Mixolydian: C major with B♭
It helps to remember which white key starts each mode: D Dorian, E Phrygian, F Lydian, G Mixolydian. A mode on any note is that "white-key" scale moved to the note.