ISRO Missions and Discoveries

[pib] Sun’s Rotation over the Century


From UPSC perspective, the following things are important :

Prelims level: Sun’s Rotation

Mains level: Not Much

Scientists at Kodaikanal Solar Observatory have estimated how the Sun has rotated over a century from data extracted from old films and photographs that have been digitized.

Try this PYQ:

Q.Consider the following phenomena:

  1. Size of the sun at dusk
  2. Colour of the sun at dawn
  3. Moon being visible at dawn
  4. Twinkle of stars in the sky
  5. Polestar being visible in the sky

Which of the above are optical illusions?

(a) 1, 2 and 3

(b) 3, 4 and 5

(c) 1, 2 and 4

(d) 2, 3 and 5

Sun’s Rotation

  • The Sun rotates around an axis that is roughly perpendicular to the plane of the ecliptic; the Sun’s rotational axis is tilted by 7.25° from perpendicular to the ecliptic.
  • It rotates in the counterclockwise direction (when viewed from the north), the same direction that the planets rotate (and orbit around the Sun).
  • The Sun’s rotation period varies with latitude on the Sun since it is made of gas.
  • Equatorial regions rotate faster than Polar Regions.
  • The equatorial regions (latitude = 0 degrees) rotate in about 25.6 days. The regions at 60 degrees latitude rotate in about 30.9 days. Polar Regions rotate in about 36 days.

Key observations of the study

  • The Sun rotates more quickly at its equator than at its poles.
  • Over time, the Sun’s differential rotation rates cause its magnetic field to become twisted and tangled.
  • The tangles in the magnetic field lines can produce strong localized magnetic fields.
  • When the Sun’s magnetic field gets twisted, there are lots of sunspots.
  • The sunspots which form at the surface with an 11-year periodicity are the only route to probe the solar dynamo or solar magnetism inside the Sun and hence measure the variation in solar rotation.

Benefits offered

  • This estimation would help study the magnetic field generated in the interior of the Sun, which causes sunspots and results in extreme situations like the historical mini-ice age on Earth (absence of sunspots).
  • It could also help predict solar cycles and their variations in the future.

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