NASA | Using Quasars to Measure the Earth: A Brief History of VLBI - 3D

The video explains how the Earth's ground moves and wobbles on its axis, affecting the length of a day. 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 emitted by quasars to determine the relative movement of telescopes. By analyzing the time differences in wave reception, scientists can calculate the distance between telescopes and observe the Earth's movements. This technique helps understand the Earth's orientation and its subtle changes over time.

Explain how time differences in radio waves can help determine the distance between telescopes.

What can you do to find out how much the ground beneath a telescope moves?