Chart · {{ zoomHint }} to zoom · drag to pan or rotate · click an object for its details · click empty sky to mark a point, again to remove it · drag a point to move it · drag a readout to move its label, drop it back on the point to re-place it
cos H = (sin alt − sin φ sin δ) / (cos φ cos δ) · usable = overlap of [RA − H, RA + H] with the astronomical dark window (Sun below −18°), in local sidereal time