Fig5_8 Internal rotation of Sun

Fig5_8 Internal rotation of Sun

Fig. 5.8 . The rotation rate inside the Sun, determined by helioseismology using instruments aboard the SOlar and Heliospheric Observatory, or SOHO for short. The outer parts of the Sun exhibit differential rotation, with material at high solar latitudes rotating more slowly than equatorial ones. This differential rotation persists to the bottom of the convective zone at 28.7 percent of the way down to the center of the Sun. The rotation period in days is given at the left axis, and the corresponding angular velocity scale is on the right axis in units of nanoHertz, abbreviated nHz, where 1 nHz = 10-9 Hz, or a billionth, of a cycle per second. A rotation rate of 320 nHz corresponds to a period of about 36 days (solar poles), and a rate of 460 nHz to a period of about 25 days (solar equator). The rotation in the outer parts of the Sun is given at latitudes of zero (solar equator), 30, 45, 60 and 75 degrees. Just below the convective zone, the rotational speed changes markedly, and shearing motions along this interface may be the dynamo source of the Sun’s magnetism. There is uniform rotation in the radiative zone, from the base of the convective zone at 0.713 solar radii to about 0.25 solar radii. The sound waves do not reach the central part of the energy-generating core. (Courtesy of Alexander G. Kosovichev/convective zone/Sebastien Couvidat, Rafael García and Sylvaine Turck-Chièze/radiative zone. SOHO is a project of international cooperation between ESA and NASA.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University