piano scale
G♯ Lydian
G♯1A♯2B♯3C𝄪♯4D♯5E♯6F𝄪7
Major with a raised fourth. The fourth mode of the major scale.
The same sounds spelled from the other side are A♭ 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♯WC𝄪HD♯WE♯WF𝄪HG♯
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.
Written correctly it needs 9 alterations, C𝄪 and F𝄪 among them. That is what the letters force, and it is also why nobody writes music in this key: the same notes spelled from the other side are easier to read.
On the same tonic, G♯ major differs from it by exactly one note.
Chords made only of these notes
Found by testing every chord in the catalogue against these 7 sounds, not chosen.