In a groundbreaking discovery, Indian astronomers have mapped the variation in the rotation speed of the Sun’s chromosphere from the equator to the poles using 100 years of data from the Kodaikanal Solar Observatory. The Observatory is just one of two such places in the entire world with such long-term data analysis of which has marked a significant advance in solar studies.

Shedding light on the Sun’s inner working, the research team from the Indian Institute of Astrophysics (IIA), an autonomous institute of Department of Science and Technology (DST) found that unlike Earth, which spins at the same speed everywhere — irrespective of the location— the Sun rotates faster at its equator than its poles. That is, in other words, about 25 days at the equator compared to 35 days at the poles.

While the phenomenon of differential rotation was first observed by Carrington in the 19th century through sunspots, this new study, “Equator to Pole Solar Chromospheric Differential Rotation Using Ca-K Features Derived from Kodaikanal Data”, utilised solar plages and network features to measure rotation speeds at higher latitudes, filling in gaps left by previous methods.

These features, captured at a specific wavelength, are continuously present and larger than sunspots, allowing for consistent data collection across the solar cycle.

By analysing the digitised data, the discovered that the rotation rate decreases from 13.98 degrees per day at the equator to 10.5 degrees per day at 80 degrees latitude. Both plages and network features exhibited similar rotation rates, suggesting a shared origin within the Sun's interior.