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The spat (symbol S) is also an obsolete unit of distance used in astronomy. It is equal to 1000000000 kilometres (1 Tm or 1012 m). It is about 6.6846 astronomical units (AU), 1.057×10−4 light-years or3.240×10−5 parsecs.
Earth radius is the distance from Earth's center to its surface, about 6,371 km (3,959 mi). This length is also used as a unit of distance, especially in astronomy and geology, where it is usually denoted by R⊕.