Measuring Method Navigating Through Space Precisely

Researchers from TU Munich and the University of Bonn (Germany) have developed a globally unique measuring method to determine fluctuations in the Earth's axis. For this, they use a single device instead of multiple telescopes around the world.

As the Earth moves through space, it wobbles slightly. A team of researchers from the Technical University of Munich (TUM) and the University of Bonn has now succeeded in measuring these fluctuations of the Earth's axis using a completely new method—previously, this was only possible through complex radio astronomy. The team used the highly precise ring laser at TUM's geodetic observatory in Wettzell, Germany.

We have achieved significant progress in Earth measurement. What our ring laser can do is unique worldwide. We are 100 times more accurate than was previously possible with gyroscopes or other ring lasers.

Prof. K. Ulrich Schreiber from the Institute of Engineering for Astronomical and Physical Geodesy at TUM

The results of the 250-day experiment were published in the renowned scientific journal Science Advances. Lead author Prof. K. Ulrich Schreiber from the TUM's Institute of Astronomical and Physical Geodesy emphasizes: "We have achieved a significant advancement in Earth's measurement. What our ring laser can do is unique worldwide. We are 100 times more precise than was previously possible with gyroscopes or other ring lasers. The exact measurement of fluctuations aids in understanding and precisely modeling the Earth system."

Why the Earth wobbles

In reality, the Earth's axis is not fixed in the sky like on a globe. Various forces act upon it, causing it to wobble to varying degrees. The strongest influence comes from the Earth's not perfectly round shape; it is slightly thicker at the equator than at the poles. This effect, known as precession, causes the extension of the Earth's axis in the sky to describe a circle. Currently, it points directly at the North Star, but in the future, it will align with other stars before returning to the North Star in a 26,000-year cycle.

Additionally, the gravitational forces of the Sun and Moon, which sometimes reinforce or cancel each other out, tug at the Earth's axis. This effect, known as nutation, causes smaller wave-like oscillations in the precession circle of the Earth's axis. There is a prominent nutation with an 18.6-year period, but also many smaller ones with fluctuations over weeks or days. As a result, the axis does not wobble evenly but rather varies in intensity over time.

Ring laser with unprecedented precision

The ring laser was able to measure all these effects directly and continuously over 250 days with unprecedented accuracy for inertial sensors, which operate independently of external signals.

Unlike before, this does not require a network of multiple large radio telescopes (VLBI) across different continents. The ring laser can achieve all of this on its own within a relatively small instrument located in an underground bunker in Wettzell. Additionally, the temporal resolution of the fluctuations is less than an hour instead of a day—and the results are available immediately rather than after days or weeks, as with VLBI.

With a future tenfold increase in the measurement accuracy and stability of the ring laser, the measurement of space-time distortion caused by Earth's rotation would come closer—a direct test of the theory of relativity. This would allow, for example, the Lense-Thirring effect, meaning the "dragging" of space by Earth's rotation, to be directly verified at Earth's surface.