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topocentric coordinates




A system of celestial coordinates with its origin at a specific point on Earth's surface. Usually, the difference in the position of an object in the sky measured using topocentric and geocentric (Earth-centered) coordinates is very small because most celestial objects are so far away. The Moon's position, however, can vary as much as 2° depending on where on Earth it is measured from, and, within the past few years, an observatory in Australia missed spotting an asteroid that passed close to Earth because it used geocentric rather than topocentric positions.


Related category

   • CELESTIAL MECHANICS