United States Naval Observatory

Gheisar Abdali

Not good

A. Seth Miller

When this was Vice President Cheney's residence, Google Maps had the entire area inside the circle blurred. It's nice to be able to see it, again. The comment about being able to look into the White House by telescope was intriguing, to say the least, and very revealing given the past residential history.

Michael X

The U.S. Naval Observatory was established in 1830 as a cartography and instrument library for the U.S. Navy. It was converted into an observatory in 1842. It is located in Foggy Bottom near the Lincoln Memorial. Its main job is to manage the U.S. Navy's marine chronometer. , nautical equipment such as nautical charts, and the astronomical clock on the ship is calibrated according to the moment when the star crosses the meridian. In 1870, American optical designer Clark built a 66-centimeter-diameter refractor telescope for the U.S. Naval Observatory. It was 13 meters long and the main mirror weighed 45 kilograms, making it the largest telescope in the world at that time. In 1877, American astronomer Assaf Hall used this telescope to discover the two moons of Mars, Phobos (Phobos) and Deimos (Demos). In 1893, the observatory moved to its current location in the Georgetown area. The first director of the U.S. Naval Observatory was U.S. Navy officer and renowned oceanographer Matthew Fontaine Maury. During his tenure, the observatory used America's first timekeeping ball to provide precise timekeeping services and telegraphed it to all parts of the United States for use by shipping, railroads, and more. In September 1913, the Paris Observatory in France used the Eiffel Tower as an antenna to receive radio signals from the U.S. Naval Observatory, and accurately measured the longitude difference between the two places [1]. Today, the U.S. Naval Observatory continues its tradition and is still one of the most authoritative institutions in the world in the field of timing and astrometry, compiling and publishing an annual astronomical calendar. Timing services provided by the US Naval Observatory can be obtained by calling or accessing the Internet [2]. The U.S. Naval Observatory's observatory near Flagstaff, Arizona uses a high-precision measuring instrument (PMM) to organize and publish the U.S. Naval Observatory's star catalog. Among them, the USNO-B1.0 star etc., self-propelled and other data, the limit star magnitude is 21, and the capacity exceeds 80GB. The USNO-A2.0 catalog contains more than 500 million stars. Its subset, the USNO-SA2.0 catalog, contains about 50 million stars for less demanding use. These catalogs are all freely available on the Internet [3].