Using 100 years daily records of the Sun at the Kodaikanal Solar Observatory, astronomers have succeeded in mapping, for the very first time, the variation in the rotation speed of the Sun’s chromosphere, from the equator right up to its polar regions.
Key facts
- Earth spins like a rigid ball, completing a full rotation every 24 hours. This rotation is the same everywhere on Earth, from bustling Bangalore to the icy plains of Antarctica.
- The Sun, however, has a completely different story to tell. Being a giant ball of plasma, different parts of the Sun rotate at different speeds, depending on their latitude.
- It has been known for a long time that the Sun’s equator spins much faster than its poles. It takes the equatorial region only about 25 days to complete one rotation, while the poles take a leisurely 35 days.
- This difference in rotation speed is called differential rotation. This is because the interaction of differential rotation with the Sun’s magnetic field is what is behind the solar dynamo, the 11-year solar cycle, and its periods of intense activity that even produce magnetic storms on Earth.
- The discovery of differential rotation dates back to Carrington in the 19th century, who observed that sunspots on the visible surface of the Sun rotated at different speeds depending on their latitude.
- Images captured at the specific wavelength of 393.3 nanometers (due to the Calcium K spectral line) showcase the lower and middle chromosphere and display prominent features like plages (bright regions) and network cells (convective structures).
- Plages, unlike sunspots, are brighter regions with weaker magnetic fields. They reside in the chromosphere, and are significantly larger than sunspots, ranging from 3 to 10 times the size of sunspots.
