piano scale
G♭ Lydian
G♭1A♭2B♭3C♯4D♭5E♭6F7
Major with a raised fourth. The fourth mode of the major scale.
The same sounds spelled from the other side are F♯ Lydian.
Written out
Every accidental is written in, rather than left to a key signature, so the letters can be read one at a time.
The step pattern
G♭WA♭WB♭WCHD♭WE♭WFHG♭
What is true of it
G♭ Lydian is G♭, A♭, B♭, C, D♭, E♭ and F, and back to G♭.
Its steps are W – W – W – H – W – W – H, where W is a whole step and H a half.
On the same tonic, G♭ major differs from it by exactly one note.
Chords made only of these notes
CdimdiminishedCm7♭5half-diminished seventhD♭majorD♭maj7major seventhE♭mminorE♭m7minor seventhFmminorFm7minor seventh
Found by testing every chord in the catalogue against these 7 sounds, not chosen.