Why the Sun’s Poles Shine Brighter: Indian Study
Why in News?
- On 12 October 2026, the Ministry of Science and Technology shared a study by Indian astronomers on why the Sun's poles shine much brighter than the rest of the solar disk at radio wavelengths.
- The team came from the Aryabhatta Research Institute of Observational Sciences in Nainital, the Udaipur Solar Observatory, Mahatma Jyotiba Phule Rohilkhand University, and IITs Delhi, Gandhinagar and Roorkee.
- They analysed nearly three decades of observations from the Nobeyama Radioheliograph in Japan, which images the Sun's full surface at radio wavelengths.
- The results were published in The Astrophysical Journal of the American Astronomical Society.
- The brightening correlates strongly with the size of polar coronal holes, and even more strongly with the strength of the polar magnetic field.
Key Terminologies
- Polar brightening
- The extra radio brightness seen over the Sun's north and south poles compared with the rest of the solar disk. The study measures how it changes over about three decades.
- Coronal hole
- A region of the Sun's outer atmosphere where the magnetic field is open. Polar coronal holes sit over the poles, and their size varies over time.
- Coronal bright points and jets
- Small bright patches inside coronal holes and the narrow streams linked to them. Many small bright patches in the study coincide with coronal bright points, and some are linked to coronal jets.
- Radioheliograph
- A radio telescope that images the whole Sun. The Nobeyama Radioheliograph in Japan provided the long record that the Indian team used.
Key Issues
- Different Poles: The study found that long-term changes in microwave polar brightening differ between the Sun's north and south poles, as do changes in polar coronal hole area.
- Hole Size Link: Brightening correlates strongly with the area of polar coronal holes. This ties a visible feature to the radio signal.
- Magnetic Field Link: An even stronger relationship was seen with the strength of the polar magnetic field, measured at the Wilcox Solar Observatory in California.
- Small-Scale Sources: Many small bright patches coincide with coronal bright points inside polar coronal holes, and some are linked to coronal jets. The images came from NASA's Solar Dynamics Observatory.
- Two Processes: The team concludes that both large-scale and small-scale magnetic processes appear to drive the brightening. A single cause does not explain it.
Key Implications
Positive/Pros/Merits
- Long Record: Nearly three decades of Nobeyama data span a period longer than two solar cycles, which is an inference, so slow changes can be seen.
- Multi-Instrument Check: The team combined radio, extreme-ultraviolet and magnetic data from three observatories, which strengthens the link between brightness and magnetic field.
- Indian Capacity: Six Indian institutions worked together, which shows national strength in solar physics beyond space missions.
Negative/Cons/Demerits
- Foreign Data Dependence: The core radio record comes from a Japanese telescope, and other data from NASA and a Californian observatory. India has no long radio record of its own to match.
- No Single Cause: The finding of both large and small-scale processes leaves open which dominates. The article reports no numerical values from the analysis.
- Correlation Only: A strong correlation shows association and does not alone prove the mechanism of heating. This is an inference.
Key Initiatives
- Ministry of Science and Technology, 12 October 2026: It shared the study, led by Indian institutions, and published it in The Astrophysical Journal.
- Aditya-L1: The Indian Space Research Organisation launched India's solar observatory on 2 September 2023 and placed it in a halo orbit around Sun-Earth L1 on 6 January 2024. It carries seven instruments, including the Visible Emission Line Coronagraph.
- Aditya-L1 Objectives: It studies the heating of the chromosphere and corona, the origin of coronal mass ejections and flares, and the solar wind, which drives space weather.
- Nobeyama Radioheliograph, Japan: It supplied nearly three decades of full-disk radio images used in the study.
- NASA Solar Dynamics Observatory: Its extreme-ultraviolet images were used to examine bright patches in the polar regions.
The Ministry of Science and Technology says the study shows that both large-scale and small-scale magnetic processes drive polar brightening. Aditya-L1 is India's own observatory for the Sun and studies the corona, the solar wind and space weather from the L1 point.
Director's Perspective
Way Forward
- Build a long Indian radio record of the Sun, so future studies can rely on home-grown data.
- Combine Aditya-L1 coronal observations with the polar brightening record to test the mechanisms the team proposes.
- Publish the numerical results and the data in open archives, so other researchers can reproduce the correlations.
The study is a solid contribution to solar physics and a good example of Indian institutions working together on long data. It ties polar brightness to coronal holes and, more strongly, to the polar magnetic field, and it points to two processes. Its limits are dependence on foreign data and the lack of published numbers in the report. In a Mains answer, credit the collaboration and Aditya-L1, then conclude that India needs its own long-term solar datasets.
GS Relevance
Frequently Asked Questions
What did the Indian study on the Sun's poles find?
The study found that the brightening of the Sun's poles at radio wavelengths correlates strongly with the size of polar coronal holes and even more strongly with the strength of the polar magnetic field. It also found that large-scale and small-scale magnetic processes both appear to drive it.
Which institutions carried out the study?
The study involved the Aryabhatta Research Institute of Observational Sciences in Nainital, the Udaipur Solar Observatory, Mahatma Jyotiba Phule Rohilkhand University, and IITs Delhi, Gandhinagar and Roorkee. The Ministry of Science and Technology shared it on 12 October 2026, and it appeared in The Astrophysical Journal.
What is Aditya-L1?
Aditya-L1 is India's solar observatory, launched by the Indian Space Research Organisation on 2 September 2023 and placed in a halo orbit around Sun-Earth L1 on 6 January 2024. It carries seven instruments to study the corona, the chromosphere and the solar wind.
PYQ Practice — Statement Analysis
1 Aditya-L1 was placed in a halo orbit around the Sun-Earth L1 point on 6 January 2024.
It was launched on 2 September 2023 on PSLV-C57.
2 The Nobeyama Radioheliograph used in the 2026 study is an Indian instrument.
It is located in Japan and images the Sun at radio wavelengths.
3 The study found that polar brightening correlates most strongly with the Sun's polar magnetic field.
It also correlates strongly with polar coronal hole size.