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.

What is a common misconception about the Earth's movement?

• The Earth rotates in a square pattern.

• The Earth does not rotate at all.

• The Earth moves in a straight line.

• The Earth only moves during earthquakes.

What is the primary purpose of Very Long Baseline Interferometry (VLBI)?

• To calculate the speed of light.

• To measure the Earth's temperature.

• To take pictures of quasars.

• To measure the distance between stars.

How does VLBI help in understanding the movement of telescopes?

• By measuring the color of quasars.

• By analyzing the time differences in radio waves.

• By counting the number of quasars.

• By observing the brightness of stars.

What can VLBI reveal about the Earth's axis?

• It moves in a circular path.

• It is perfectly stable.

• It is fixed in one position.

• It wobbles as the Earth revolves around the sun.

What humorous suggestion is made about checking if your house has moved?

• Using a compass.

• Switching on a bunch of radio telescopes.

• Measuring with a ruler.

• Asking a neighbor.