Differential Rotation of the Sun

Does the Sun Rotate?

Introduction

Yes, the Sun rotates about its axis, but its rotation is differential, meaning different parts of the Sun rotate at different rates. This phenomenon is significantly different from the Earth's uniform rotation.

Key Features of the Sun’s Rotation

1.     Differential Rotation:

o    Equator: Rotational period is approximately 26.5 days.

o    Sunspot Zone (16° North): Rotational period increases slightly to 27.3 days.

o    Poles: Rotational period is longest at about 31.1 days.

o    This variation in rotation speed is due to the Sun's composition being in a plasma state, unlike the solid Earth.

2.     Plasma State of the Sun:

o    The Sun’s core temperature reaches 15 million K, and its surface temperature is about 6,000 K.

o    These extreme conditions keep the Sun's constituents in a high-pressure, gaseous state, or plasma, allowing its layers to rotate at varying speeds.

3.     Designation of Poles:

o    The top and bottom of the Sun’s visible sphere are referred to as the north and south poles, for ease of calculations in solar studies.

Methodology to Study the Sun’s Rotation

• Observation of Surface Features:
• Daily photographs are taken to track the movements of sunspots, filaments, and plages (bright regions on the Sun’s surface).
• Observations are conducted over varying latitudes and longitudes over extended periods.
• Calculation of Sidereal Rotation Period:
• Based on these observations, the sidereal rotation period (the time it takes for the Sun to complete one rotation relative to distant stars) is calculated.

Scientific Mystery

The exact cause of the Sun’s differential rotation remains an unresolved puzzle for solar physicists. Potential areas of inquiry include:

• The role of magnetic fields.
• The interaction between the Sun’s plasma layers.
• The influence of its internal convection zones.

Conclusion

The Sun’s differential rotation underscores the complexity of stellar dynamics, particularly in stars composed of plasma. Advances in solar physics, aided by space-based observations and computational models, may eventually unravel this mystery. Understanding this phenomenon is critical, as it has implications for solar activity cycles, including sunspots and solar flares, which can impact Earth.

MCQs on the Sun’s Rotation

Q1. The Sun’s rotation is different from Earth’s rotation because:

1.     The Sun is in a plasma state, allowing differential rotation.

2.     The Sun’s rotation period is uniform across all latitudes.

3.     The Sun’s surface features move at varying speeds due to its composition.

Select the correct answer:

• (a) 1 and 2 only
• (b) 1 and 3 only
• (c) 2 and 3 only
• (d) 1, 2, and 3

Answer: (b) 1 and 3 only

Q2. What is the approximate rotational period of the Sun near its equator?

• (a) 26.5 days
• (b) 27.3 days
• (c) 31.1 days
• (d) 24 hours

Answer: (a) 26.5 days

Q3. Which of the following features are tracked to calculate the Sun’s sidereal rotation period?

1.     Sunspots

2.     Filaments

3.     Plages

Select the correct answer:

• (a) 1 only
• (b) 1 and 2 only
• (c) 1, 2, and 3
• (d) None of the above

Answer: (c) 1, 2, and 3

Q4. What is the state of matter of the Sun’s constituents?

• (a) Solid
• (b) Liquid
• (c) Plasma
• (d) Gas

Answer: (c) Plasma

Q5. Why is the Sun’s rotation referred to as “differential”?

1.     Different parts of the Sun rotate at different speeds.

2.     The Sun has the same rotation period at all latitudes.

3.     Plasma composition allows variations in rotational velocity.

Select the correct answer:

• (a) 1 and 3 only
• (b) 2 and 3 only
• (c) 1 only
• (d) 1, 2, and 3

Answer: (a) 1 and 3 only