interval
F♯ major sixth
F♯lowerD♯upperM69 half steps
Nine half steps. The minor third turned upside down.
On the keyboard
What is true of it
F♯ up a major sixth is D♯: 9 half steps, and 6 letters counting both ends.
Turn it upside down — put the F♯ on top — and it becomes a minor third. The two numbers always add to nine, and the two sizes to twelve.
It is a imperfect consonance.
Every interval on F♯
F♯ → Gminor second · dissonanceF♯ → G♯major second · dissonanceF♯ → Aminor third · imperfect consonanceF♯ → A♯major third · imperfect consonanceF♯ → Bperfect fourth · perfect consonanceF♯ → B♯augmented fourth · dissonanceF♯ → Cdiminished fifth · dissonanceF♯ → C♯perfect fifth · perfect consonanceF♯ → Dminor sixth · imperfect consonanceF♯ → Eminor seventh · dissonanceF♯ → E♯major seventh · dissonance