Turning Dish Antennas To The Sun: Indian Scientists Pioneer Low-Cost Solar Magnetic Field Mapping

Bengaluru: In a groundbreaking development, scientists at the Indian Institute of Astrophysics (IIA), Bangalore, have demonstrated that commercial dish TV antennas—typically used to receive satellite television signals—can be ingeniously repurposed to study the magnetic field of the Sun. This low-cost, scalable approach has the potential to revolutionise the way solar magnetic fields are observed and monitored, from the Sun’s visible surface to the outermost layers of its atmosphere with ground-based facilities.

Traditionally, measurements of the Sun’s magnetic field at its surface, known as the photosphere, are performed routinely using sophisticated ground-based and space-based telescopes employing optical techniques. However, tracking how these magnetic fields extend beyond the photosphere into the Sun’s higher atmospheric layers—namely, the chromosphere and the corona—has remained a significant challenge. This is especially critical because many high-energy solar phenomena—such as solar flares, quakes and eruptions, and Coronal Mass Ejections (CMEs)—originate in the chromosphere and corona.

On the Sun's photosphere, there are dark regions called Sunspots, caused by intense magnetic fields that inhibit the flow of heat from the inside layers, making them cooler than the surrounding areas. Magnetic field lines are regions where highly charged particles, such as electrons and ions, are confined. These magnetic field lines form large loops that extend from the photosphere through the chromosphere into the corona and even out into interplanetary space. When magnetic reconnection occurs between the loops, it triggers solar flares and plasma ejection, releasing a large amount of energy.

Understanding this complete structure and evolution of solar magnetic fields, from the photosphere to the corona, is key to predicting space weather, an area of study that focuses on solar-driven disturbances in Earth’s space environment. These disturbances can disrupt satellite operations, affect spacecraft systems, and even damage power grids on Earth. Consequently, enhancing our ability to measure and monitor the Sun’s magnetic field in a continuous and cost-effective manner is not just a scientific necessity, but also a technological imperative.

A New Idea Born from Serendipity

At the heart of this breakthrough is IIA’s Gauribidanur Radio Astronomy Field Station, located near Bangalore. This facility has long been a global hub for observing the solar corona and its magnetic activity through radio astronomy. However, the idea of using dish antennas—commonly found on rooftops across India—emerged unexpectedly. During a technical discussion, scientists were examining signals from regions of the sky that overlapped with TV transmitter directions. When one such direction coincided with the Sun’s position, they observed a sudden spike in the signal. This surprising result led to the hypothesis: could commercial dish antennas detect solar emissions?

Upon further investigation, the answer was a resounding Yes.

Innovation lies: Radio Emissions from the Chromosphere-

While the photosphere is visible and relatively easier to study, the chromosphere, which lies just above it, is far more elusive. It spans roughly 2,000 km in thickness and is often hidden from view by the intense brightness of the photosphere. Above the chromosphere lies the solar corona—the outermost part of the Sun’s atmosphere. Corona is visible only during a total solar eclipse or through specialised instruments.

In an interview with ETV Bharat, R Ramesh, Senior Professor at IIA, Principal Investigator for the VELC instrument aboard ISRO’s Aditya-L1 mission, and Head of the Gauribidanur facility talked how it all works and said, “Interestingly, the chromosphere emits radio waves at specific frequencies, especially around 11.2 GHz, due to two main processes: thermal bremsstrahlung (free-free emission) and gyroresonance. These emissions can be captured by dish antennas designed to receive satellite television signals. When reoriented toward the Sun, these antennas act as radio receivers, capturing emissions directly from the chromospheric layer.”

The commercial dish TV antenna set-up in the Gauribidanur radio astronomy field station, used for measurements of the magnetic field in the Sun’s chromosphere. (Special Arrangement)

This is where innovation lies. Unlike optical techniques, which are limited by atmospheric conditions like cloud cover or require expensive space-based instruments, radio astronomy is far more resilient. Radio waves at these frequencies can pass through clouds, making observations possible even during monsoons or in overcast weather. This allows year-round, uninterrupted monitoring of the Sun’s magnetic behaviour from the ground itself.

Affordable and Scalable Technology

Professor Ramesh explained the motivation behind this innovation. “Astronomy is a subject where large investments are often required to carry out even basic investigations. We wanted a cost-effective and simple tool—something that could be purchased off the shelf.”

The entire system, developed in-house at IIA, was built for approximately ₹20 lakh—a small fraction of the cost of conventional telescopes. Moreover, the antennas used in the project were fabricated in IIA’s own workshop in Gauribidanur, demonstrating the feasibility of producing and deploying such instruments locally, aligning with the Atmanirbhar Bharat vision of self-reliant scientific advancement.

Scientific Advantages and Limitations

Discussing the advantages and challenges, the Professor said that traditionally, the magnetic field in the chromosphere is difficult to measure due to its complex and dynamic behaviour. Optical methods rely on spectral lines emitted by the chromosphere, which are highly sensitive to the Sun's temperature near the region of emission and observing conditions.

In contrast, radio techniques provide a cleaner and more stable signal, with significantly fewer environmental constraints. However, radio observations come with their own limitations: emissions at different frequencies originate from different layers of the solar atmosphere.

While the Gauribidanur facility is well-suited for low-frequency observations of the corona, studying the chromosphere demands instruments operating in the GHz frequency range—such as those now demonstrated using commercial dish antennas. By observing the Sun simultaneously at multiple frequencies, researchers can reconstruct a three-dimensional view of solar activity—an excellent example of transforming a challenge into an advantage.

Professor Ramesh emphasised that for solar radio observations, antenna size is not a critical constraint. Instead, increasing the number of antennas—or receivers—enables the system to be scaled up for continuous, real-time monitoring. These antennas can be deployed anywhere, making the system ideal for expanding solar observation networks across educational and research institutions.

Integration with Aditya-L1 and Broader Applications

As Principal Investigator of the VELC (Visible Emission Line Coronagraph) payload on ISRO’s Aditya-L1 solar mission, Ramesh noted that data from VELC will be used in conjunction with observations from Gauribidanur and the dish antenna array. By separating and comparing signals layer by layer—from the chromosphere to the corona—scientists can gain a comprehensive view of solar activity and its underlying magnetic processes.

This illustration lays a depiction of the sun’s magnetic fields over an image captured by NASA’s Solar Dynamics Observatory on March 12, 2016. (Credits: NASA/SDO/AIA/LMSAL)

This synergy opens up a new frontier in solar atmospheric studies. Early detection of rising magnetic fields/loops from the photosphere, long before they erupt into full-fledged CMEs in the corona, becomes possible. Such early warnings are essential for protecting satellites, spacecraft, and terrestrial infrastructure from the disruptive effects of space weather.

In addition, these dish antennas have further potential. They can be directly calibrated using observations of planetary bodies like the Moon, adding to their scientific versatility.

Educational Impact and Student Involvement

Professor Ramesh said that the project has also provided valuable hands-on learning opportunities for students. Engineering students from BMS College of Engineering and Amrita Vishwa Vidyapeetham (Bangalore campus) were actively involved in building and testing the hardware and software systems. Their participation underscores the project’s educational impact and highlights how accessible tools can foster meaningful scientific engagement.

This model can be replicated by other educational institutions to establish their own radio astronomy labs, enabling undergraduate and postgraduate students to engage directly with frontline research.

A Tribute to Serendipitous Science

Ramesh compared this unexpected discovery to one of the most iconic moments in modern astronomy: the accidental detection of the Cosmic Microwave Background (CMB) by Arno Penzias and Robert Wilson in 1965. While testing a horn antenna at Bell Labs, they detected an unexplained signal—later identified as the thermal relic of the Big Bang. Their discovery earned them the Nobel Prize in Physics and provided crucial evidence for the Big Bang theory.

“Sometimes, great science happens by chance,” Professor Ramesh remarked, “provided one is willing to investigate the anomalies.”

According to the study, this novel use of commercial dish antennas enhances our ability to monitor and predict space weather events that could affect global communications and power infrastructure. By integrating these observations with missions like Aditya-L1 and involving students in hands-on projects, India might be setting an example in scientific innovation, education, and self-reliance.