Contrary to common belief, Earth’s rotation does not adhere to a precise 24-hour cycle. This inconsistency is attributed to the Earth’s heterogeneous composition – a blend of various solids and liquids, each influencing the planet’s rotational speed.
“Fluctuations in rotation are not only important for astronomy, we also urgently need them to create accurate climate models and to better understand weather phenomena like El Niño,” said Ulrich Schreiber, the project lead at the Observatory for TUM. “And the more precise the data, the more accurate the predictions.”
TUM’s breakthrough centers on the enhancement of a ring laser, a sophisticated device capable of measuring the Earth’s rotation with remarkable precision.
This laser, housed within the Geodetic Observatory Wettzell, operates within a specially designed pressurized chamber buried 20 feet underground. It comprises a laser ring gyroscope and a 13.1-foot-wide “racetrack,” all meticulously calibrated to ensure that external factors minimally influence the laser’s readings.
The device uses a complex system of lasers and mirrors to accurately detect variances in the speed of Earth’s rotation. These differences are indicated by the fluctuating frequencies between two laser beams, with larger discrepancies signifying faster rotation.
For instance, at the equator, where the Earth rotates at 15 degrees per hour, the ring laser records a frequency of 348.5 Hz, which subtly changes by mere millionths of a Hertz daily.
However, achieving exact measurements with this technology is challenging due to the inherent asymmetry in the device’s design.
Over the past four years, geodesists have developed a theoretical model for laser oscillations to account for these systematic effects.
By incorporating a corrective algorithm, they can now precisely eliminate these discrepancies from their measurements, enabling them to measure Earth’s rotation to an astonishing nine decimal places. This equates to a variance of approximately a fraction of a millisecond each day.
“In geosciences, time resolution levels this high are absolutely novel for standalone ring lasers. In contrast to other systems, the laser functions completely independently and doesn’t require reference points in space,” said Professor Urs Hugentobler.
“With conventional systems, these reference points are created by observing the stars or using satellite data. But we’re independent of that kind of thing and also extremely precise.”
Interestingly, the Earth’s day length has been gradually increasing over time. During the era of the dinosaurs, a day lasted only 23 hours, and 1.4 billion years ago, it was a mere 18 hours and 41 minutes.
Projections suggest that in 200 million years, a day will extend to 25 hours. This evolving dynamic of Earth’s rotation underscores the importance of advanced measurements, though it leaves one to wonder who or what might be around to witness these changes in the distant future.
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