English: Personnel at the U.S. Naval Observatory in Washington, D.C., prepare the facility's historic 26-inch refractor telescope for optical viewing of Mars. The telescope is the same one that discovered Phobos and Deimos, the two moons of Mars, in 1877. The telescope, which still uses the original optics, normally has a camera known as a speckle interferometer mounted in the viewing position for deep space studies. The United States Naval Observatory (USNO) performs an essential scientific role for the U.S. Navy, and Department of Defense (DOD). Its mission includes determining the positions and motions of the Earth, Sun, Moon, planets, stars, and other celestial objects; providing astronomical reference data; measuring the Earth’s rotation and orientation; determining precise time; and maintaining the Master Clock for the United States. U.S. Navy photo by Chief Warrant Officer 4 Seth Rossman