Question

what were sextants, which used celestial bodies like stars to plot courses of movement and exploration, used for?
astronavigation
fusion
emission lines
parallax

Explanation:

A sextant is a navigational instrument. It measures the angular distance between two visible objects. In astronavigation, it measures the angle between a celestial body (like a star) and the horizon. This helps in determining a ship's or aircraft's position. Fusion is a nuclear process. Emission lines are related to spectroscopy. Parallax is a displacement - angle measurement method but not the main use of a sextant.

Answer:

astronavigation