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How we will able to determine the size of astronomical unit of diameter of a moon or a planet ? |
| Answer» The astronomical unit (symbol: AU) is a unit of length, roughly the distance from Earth to the Sun and equal to about 150 million kilometres (93 million miles). However, that distance varies as Earth orbits the Sun, from a maximum (aphelion) to a minimum (perihelion) and back again once a year. The most common is to\xa0measure\xa0the apparent angular diameter of the\xa0planet\xa0– how big it looks against the sky – very precisely using a telescope. Combining this with a\xa0measure\xa0of its distance (deduced from its orbit around the Sun) reveals the\xa0planet\'s\xa0actual\xa0size. | |