C# major is a major scale based on C#, consisting of the pitches C#, D#, E#, F#, G#, A#, B# (enharmonic to C natural) and C#. Its key signature consists of seven sharps.
Ascending and descending C-sharp Major Scale
Its relative minor is A-sharp minor, and its parallel minor is C-sharp minor. Its enharmonic equivalent is D-flat major.
A harp tuned to C-sharp major has all its pedals in the bottom position. Because all the strings are then pinched and shortened, this is the least resonant key for the instrument.
Although most composers prefer to use the enharmonic equivalent D-flat major because it has just five flats as opposed to the seven sharps of C-sharp major, Johann Sebastian Bach actually chose C-sharp major for Prelude and Fugue No. 3 in both books of the Well-Tempered Clavier. Béla Bartók's String Quartet No. 3 is one of the few in C-sharp major.