Century-old Kodaikanal Observatory images reveal Sun's past polar magnetic fields
Astronomers led by the Aryabhatta Research Institute of Observational Sciences (ARIES) have reconstructed the Sun's polar magnetic fields over the past century using historical images from the Kodaikanal Solar Observatory, DST said on 19 November 2025.
Summary
The ARIES-led team, headed by Dibya Kirti Mishra, used Ca II K images that the Kodaikanal Solar Observatory (KoSO) has recorded since 1904, along with Italy's Rome-PSPT data, to track tiny bright features near the Sun's poles called the polar network. This served as a proxy for polar field strength over 1904â2022, filling the gap before direct measurements began in the 1970s, and was used to estimate the strength of the ongoing Solar Cycle 25. KoSO is a field station of the Indian Institute of Astrophysics, Bengaluru, and the data are freely available on GitHub and Zenodo.
Key facts
- Lead institute
- ARIES (DST)
- Data
- Kodaikanal Solar Observatory Ca II K images since 1904
- Proxy
- Polar network → polar magnetic field
- Period reconstructed
- 1904â2022
- Application
- Estimate of Solar Cycle 25 strength
- KoSO
- Field station of IIA, Bengaluru
Practice MCQs 2 questions
Which institute led the study that reconstructed the Sun's past polar magnetic fields using Kodaikanal Solar Observatory data (November 2025)?
Show answer
Correct answer: C â Aryabhatta Research Institute of Observational Sciences
The study was led by ARIES, an autonomous institute under DST. KoSO itself is a field station of the Indian Institute of Astrophysics.
Since which year has the Kodaikanal Solar Observatory been observing the Sun in the Ca II K wavelength?
Show answer
Correct answer: B â 1904
KoSO began observing the Sun in the Ca II K wavelength as early as 1904.