F♯ major
Key with six sharps.
What it means
F♯ major is the major key with six sharps in the key signature: F♯, C♯, G♯, D♯, A♯, and E♯. Its root is F♯, its relative minor D♯ minor. In the circle of fifths it lies six steps on the sharp side — that is, at the point where the circle meets the flat side.
Musical use
That is precisely where its special feature lies. F♯ major sounds on tempered instruments like G♭ major, which carries six flats; both spellings designate the same sound and are enharmonically equivalent. Which one is chosen is decided by the context: the harmonic path by which the key is reached, the convenience for the performers, the avoidance of double accidentals in the further course. With secondary dominants and altered sonorities, double sharps can become necessary in F♯ major.
In unequal temperaments such a remote key was difficult to unusable; only well-tempered tunings made it playable, and only equal temperament makes it equal to the others. The traditional talk of the character of remote keys has its origin here.
For string players F♯ major is uncomfortable, because no open strings are available; on the piano, by contrast, it lies quite favourably for the hand through the distribution of the black keys.
F♯ major is the relative key of D♯ minor and enharmonically equivalent to G♭ major, which carries six flats. In the circle of fifths the key lies exactly opposite the starting point C major, at the distance of a tritone. On the piano it fits the hand well, because almost only black keys are used. In the piano music of the Romantic period it often appears in luminous, rapt pieces. For strings and winds it is more uncomfortable because of the lack of open strings and difficult fingerings.
Performance practice
Say the six sharps aloud before playing and name the notes instead of merely grasping the number — E♯ is regularly read as E. With double sharps, first check the sounding note and then the fingering. And if you meet the same music in another edition as G♭ major, that is not a mistake but a decision of the editor.