GEOSCIENCE:
Ring Laser Senses Earth's Spin
Alexander Hellemans
The time it takes the Earth to make a full turn fluctuates by a few milliseconds per day because tides, atmospheric changes, and perhaps movements in the Earth's core are constantly shifting the planet's mass. Now the world's largest ring laser gyroscope, a glass block more than a meter across threaded by counterrotating laser beams, will keep track of Earth's vagaries from a cave in New Zealand.