Related Experiment Video
Updated: Jun 29, 2026

Scattering And Absorption of Light in Planetary Regoliths
Published on: July 1, 2019
A large excess in apparent solar oblateness due to surface magnetism
Martin D Fivian1, Hugh S Hudson, Robert P Lin
1Space Sciences Laboratory, University of California-Berkeley, Berkeley, CA 94720, USA. mfivian@ssl.berkeley.edu
Abstract:
The shape of the Sun subtly reflects its rotation and internal flows. The surface rotation rate, approximately 2 kilometers per second at the equator, predicts an oblateness (equator-pole radius difference) of 7.8 milli-arc seconds, or approximately 0.001%. Observations from the Reuven Ramaty High-Energy Solar Spectroscopic Imager satellite show unexpectedly large flattening, relative to the expectation from surface rotation. This excess is dominated by the quadrupole term and gives a total oblateness of 10.77 +/- 0.44 milli-arc seconds. The position of the limb correlates with a sensitive extreme ultraviolet proxy, the 284 angstrom limb brightness. We relate the larger radius values to magnetic elements in the enhanced network and use the correlation to correct for it as a systematic error term in the oblateness measurement. The corrected oblateness of the nonmagnetic Sun is 8.01 +/- 0.14 milli-arc seconds, which is near the value expected from rotation.
Related Concept Videos
Potential Due to a Magnetized Object
The vector...
Variation in Acceleration due to Gravity near the Earth's Surface
The difference between the true and apparent weights is proportional to the square of the Earth's angular speed. Since the...
Apparent Weight and the Earth's Rotation
For an object on the Earth's equator, the net centripetal force that accounts for its rotation is the Earth's pull towards its center, or the weight minus the normal force that prevents it from piercing into the Earth's surface. This force,...
Magnetic Flux
Suppose a surface is divided into elements of area dA. For each element, the component of the magnetic field that is normal to the...
Magnetism
An individual magnetic pole cannot be isolated. No matter how small, every piece of a magnet contains a north pole and a south...
Magnetic Declination
