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Answer to Question #62708 in Astronomy | Astrophysics for Aref

Question #62708
I know the old ways of measuring radius of the Earth.
But I wan't to know what is the method that for example NASA uses nowadays to measure it ?
I want to know the best and most accurate way of measuring it.
Expert's answer
Satellite laser ranging -- a global observation station network that measures, with millimeter-level precision, the time it takes for ultrashort pulses of light to travel from the ground stations to satellites specially equipped with retroreflectors and back again.

Very-long baseline interferometry -- a radio astronomy technology that combines observations of an object made simultaneously by many telescopes to simulate a telescope as big as the maximum distance between the telescopes.

Global Positioning System -- the U.S.-built space-based global navigation system that provides users around the world with precise location and time information.

Doppler Orbitography and Radiopositioning Integrated by Satellite -- a French satellite system used to determine satellite orbits and positioning. Beacons on the ground emit radio signals that are received by satellites. The movement of the satellites causes a frequency shift of the signal that can be observed to determine ground positions and other information.

Scientists currently determine this origin point based on a quarter century of satellite laser ranging data, considered the most accurate space geodetic tool for this purpose.

The scientists estimated the average change in Earth's radius to be 0.1 millimeters per year, or about the thickness of a human hair.

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