An underground gyroscope known as ‘G’ uses laser beams traveling in opposite directions to precisely measure Earth’s rotation.
Using a laser gyroscope, scientists have measured variations in Earth’s rotation rate smaller than a millionth of a percent. The technique could help scientists understand the complex flows of water and air that cause the tiniest of tweaks to the planet’s spin.
Earth’s rotation isn’t perfectly steady. The planet speeds up and slows down as it twirls, making a day slightly shorter or longer by several milliseconds. Many of those variations are well understood. For example, one such variation is caused by tidal forces, created by the gravitational pull of the moon and the sun, that deform the planet. Scientists know how to predict those effects on Earth’s rotation.
The gyroscope, known as “G” and located at the Geodetic Observatory Wettzell in Germany, is designed to measure those tiny effects. It’s what’s called a ring laser gyroscope. Within it, laser beams travel around a square-shaped ring that is 4 meters on each side. One beam circulates clockwise while another goes counterclockwise. Beams aligned with the direction of Earth’s rotation have their wavelength stretched out, while those traveling against it shrink.
G’s capabilities are unique: “It is a measurement which was considered not possible with other detectors,” says physicist Angela Di Virgilio of the National Institute for Nuclear Physics in Pisa, Italy, who was not involved with the new study. “So it is good that they have obtained some results from this impressive instrument.”
Such measurements could help scientists refine their models of Earth’s air circulation and ocean currents. In the future, scientists hope to be able to measure even more elusive effects with improved ring laser gyroscopes. According to Albert Einstein’s general theory of relativity, a rotating planet
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