Sound Waves Inside The Sun Now Reveal Magnetic Secrets On Its Hidden Far Side

by Clarence Oxford
Los Angeles CA (SPX) Apr 25, 2026
For observers on Earth, the Sun appears as a bright, familiar disk - but what we see is only half the story. Like the Moon, one half of the Sun is permanently hidden from our direct view: the far side beyond the visible solar limb. Yet, activity brewing there can eventually turn toward Earth, sometimes unleashing solar flares and eruptions capable of disrupting human technology.

A quarter of a century ago, scientists devised a way to detect these invisible threats before they rotate into view. Using a technique known as helioseismology, scientists analyze sound waves reverberating inside the Sun to locate large active regions forming on its hidden half. These methods can reveal the presence of sunspot groups days before they become visible from Earth.

"Helioseismology has allowed us to detect where active regions exist on the far side of the Sun," says Dr. Amr Hamada of the U.S. National Science Foundation National Solar Observatory (NSF NSO), lead author of the new study. "However, until recently we could not determine one of their most important properties: the magnetic polarity."

Magnetic polarity describes how magnetic fields are oriented, with positive polarity pointing outward from the Sun and negative polarity pointing inward. This structure governs how solar magnetic fields interact with their surroundings, and determines whether an eruption might produce a powerful geomagnetic storm or merely a weak one.

The breakthrough comes from new analysis of helioseismic observations collected by the NSF-NOAA Global Oscillation Network Group (NSF-NOAA GONG), built and operated by the NSO with support from the National Oceanic and Atmospheric Administration (NOAA). NSF-NOAA GONG is a worldwide network of robotic solar telescopes that continuously monitors the subtle oscillations rippling across the Sun's surface. These oscillations - caused by waves traveling through the Sun's interior - carry information about the star's internal structures and magnetic features.

"The Sun is constantly ringing with sound waves," Hamada says. "By measuring how those waves travel through the solar interior, we can learn about structures both inside the Sun, and on the far side of its surface."

"Although magnetic fields have been estimated before, the novelty here lies in the physics-driven determination of magnetic polarities and tilt angle within the helioseismically identified active regions," explains Dr. Kiran Jain, Lead Scientist of the NSO Far Side Project and a co-author on the study.

"For more than two decades, the Sun's oscillations have been used to produce far-side maps that reveal where large active regions exist. But the new work shows that the waves contain additional clues hidden in their patterns," says Dr. Alexei Pevtsov, NSO Associate Director for NSO's Synoptic Program, which is responsible for NSF-NOAA GONG operations.

By examining subtle signatures known as phase shifts in helioseismic maps, Hamada and a team of scientists from the NSO, Instituto de Astrofisica de Andalucia (Spain), and NorthWest Research Associates (USA) found they could infer how magnetic fields are arranged inside far-side regions. By carefully analyzing the structure of the phase-shift signatures and applying known dependencies such as the Hale polarity rule, the researchers can determine the magnetic polarity of active regions even though they are not directly visible.

In essence, the Sun's sound waves are not only showing where active regions exist - they are also revealing information about their magnetic structure. Using this method, the researchers can reconstruct polarity-resolved magnetograms - maps showing magnetic field orientation - for regions on the Sun's hidden hemisphere. That capability marks a major step toward a long-standing goal in solar physics: building a complete global map of the Sun's magnetic field.

Until now, solar magnetic maps have been limited to the side facing Earth. As viewed from Earth, the Sun takes about 27 days to complete one rotation, meaning active regions forming out of view can become geoeffective long before scientists can measure their magnetic structure directly. Incorporating far-side polarity data into global magnetic field models could dramatically improve predictions of solar activity.

Such improvements carry growing urgency. Solar eruptions associated with strong magnetic regions can drive space weather events capable of damaging satellites, endangering astronauts, and disrupting navigation, communications, and energy infrastructure. A more complete magnetic picture of the Sun could give forecasters earlier warnings of potentially disruptive events.

Even though the far side of the Sun is completely invisible to telescopes near Earth, the Sun's internal acoustic waves carry information from that hidden hemisphere across the solar interior. With the new technique, which combines helioseismology and known properties of magnetic fields, those solar sounds are now revealing the invisible architecture shaping the Sun's most powerful activity.

If researchers can continue refining the method, scientists may soon achieve something once thought impossible - a continuous magnetic map of the entire Sun, including the hemisphere forever hidden from direct view.

Research Report:Polarity-resolved far-side magnetograms based on helioseismic measurements