See bifocals and magnifying glasses.
Like I said, have a star map that you can clearly see. At default settings, the sextant view basically acts like a magnifying glass. Make it so that when you scroll horizontally, you scroll the star map itself and not the scope. When you scroll vertically, you control half the scope's view (similar to a real sextant).
Basically, a circle split in half. Half the circle is the horizon view. The other half of the circle is the sky view. Have it basically act like a magnifying glass in that it zooms in.
