NASA | Using Quasars to Measure the Earth: A Brief History of VLBI

The video explains how the Earth's movement is more complex than it seems, with the ground moving and the Earth wobbling on its axis. Scientists use a technique called Very Long Baseline Interferometry (VLBI) to measure these movements precisely. Originally developed to take pictures of quasars, VLBI uses radio waves to determine the relative movement of telescopes. By analyzing the time differences in radio wave reception, scientists can measure the Earth's orientation and movement. This technique reveals that days are not exactly 24 hours and that the Earth wobbles as it orbits the sun.

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