piano scale
A♭ Lydian
A♭1B♭2C3D♯4E♭5F6G7
Major with a raised fourth. The fourth mode of the major scale.
The same sounds spelled from the other side are G♯ 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
A♭WB♭WCWDHE♭WFWGHA♭
What is true of it
A♭ Lydian is A♭, B♭, C, D, E♭, F and G, and back to A♭.
Its steps are W – W – W – H – W – W – H, where W is a whole step and H a half.
On the same tonic, A♭ major differs from it by exactly one note.
Chords made only of these notes
CmminorCm7minor seventhDdimdiminishedDm7♭5half-diminished seventhE♭majorE♭maj7major seventhFmminorFm7minor seventh
Found by testing every chord in the catalogue against these 7 sounds, not chosen.