piano scale
F♯ major
F♯1G♯2A♯3B4C♯5D♯6E♯7
The seven-note scale everything else is measured against: two whole steps, a half, three whole steps, a half.
The same sounds spelled from the other side are G♭ major.
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
F♯WG♯WA♯HBWC♯WD♯WE♯HF♯
What is true of it
F♯ major is F♯, G♯, A♯, B, C♯, D♯ and E♯, and back to F♯.
Its steps are W – W – H – W – W – W – H, where W is a whole step and H a half.
It costs 6 alterations to write — near the limit of what a key signature can carry.
On the same tonic, F♯ melodic minor differs from it by exactly one note.
Chords made only of these notes
C♯majorC♯7dominant seventhD♯mminorD♯m7minor seventhF♯majorF♯maj7major seventhG♯mminorG♯m7minor seventh
Found by testing every chord in the catalogue against these 7 sounds, not chosen.