Composite image of the Sun illustrating part of the wide range of SOHO's scientific research. Left interior cutaway: Variations in the speed of sound in the deep interior as gauged by helioseismic measurements by SOHO/MDI and SOHO/VIRGO.
The conspicuous red layer, about a third of the way down from the surface to the Sun's centre, shows unexpectedly high temperatures at the transition between the turbulent outer region (convection zone) and the more stable region inside it (radiative zone). The very core of the Sun (blue) may be 0.1% cooler than the expected 15 million C. Right interior cutaway: Solar interior rotation (red: faster rotation, blue: slower rotation). The equatorial regions rotate faster than the polar regions, all the way down to the bottom of the convection zone. The radiative zone below appears to rotate at the same angular velocity (solid body rotation).
Outer cutaway: SOHO/MDI visible light image showing sunspots in the photosphere. Wrap-around: SOHO/EIT He II 304. image showing the Sun?s outer atmosphere (transition region) at a temperature of about 60,000 C.