Azimuth is an arc of the heavens extending from the zenith to the horizon which it cuts at right angles. The quadrant of a great circle of the sphere passing through the zenith and the nadir is called an azimuthal circle. In architecture, azimuth is an angle expressed in degrees on a plane view measured clockwise from due north. Along with bearing direction it one of two means of expressing the plan direction of non vertical lines. Traditionally azimuths and almucanthars were important for the construction of astrolabes.