This historical astronomical instrument was used by classical astronomers, navigators and astrologers. Its many functions enables locating and predicting the positions of the Sun, Moon, planets and stars; determining local time given local latitude and vice-versa; surveying; and triangulation. In the medieval Islamic world, they were used primarily for astronomical studies, as well as, in other areas as diverse as astrology, navigation, surveying, timekeeping and determining prayer times. Astrologers of the European nations used astrolabes to construct horoscopes.