An astronomer might use a sextant or quadrant to measure the distance between a planet and a notable bright star, or the altitude of a star above the horizon. A quadrant measures up to 90 degree angular separation (one fourth or quadrant of a circle), while a sextant measures up to 60 degree (one sixth of a circle). These instruments might be portable enough to carry outside, or monumental constructions mounted to a roof or positioned in an outdoor observatory.