Largest astronomical observatory site

Timelapse photography reveals Earth’s rotation, which takes 23 hours, 56 minutes and 4.06 seconds to spin once around its axis. This is slightly shorter than the traditional 24-hour day, measured from noon to noon and affected by the movement of Earth around the Sun. One true rotation is measured by the stars and Earth has the shortest "sidereal" day of the inner planets. The star trails caused by the long exposure are shortest towards the north pole of the sky, here hidden behind the Canada-France-Hawaii Telescope. This is one of 13 working telescopes on the summit of Hawaii’s Mauna Kea, collectively forming the world’s largest astronomical observatory site. Largest is here defined by as "largest concentration of major observatories in the world".