Which of the following best describes what determines the shape of the corona?

• A. The Sun's magnetic field.
• B. The solar wind speed.
• C. The temperature of the photosphere.
• D. The planets' gravity.

Answer: (A)

The shape of the corona is set by the Sun’s magnetic field. In the corona, the plasma is highly conductive, so it moves along magnetic field lines. Where the field lines are closed loops near active regions, the corona forms bright, looping structures. Where lines open into space, coronal holes appear and the solar wind streams freely outward. The overall outline of the corona follows this magnetic topology, which changes with the solar activity cycle, producing different global shapes.

The other factors don’t determine the geometry as directly. Solar wind speed depends on heating and field topology and is a consequence, not the driver, of the corona’s shape. The photosphere’s temperature affects brightness and emission details but not the large-scale structure. Planets’ gravity is far too weak to shape the Sun’s corona.