Sun's interior. Computer model of the variations in the speed of sound in the Sun, based on data taken by the SOHO (Solar and Heliospheric Observatory) spacecraft. The colours in the cut- away portion of the Sun show the observed speed of sound relative to the speed predicted by a theoretical solar model. Red regions have a higher speed of sound than expected, and in blue regions it is lower than expected. This indicates that the red and blue regions are respectively hotter and cooler than predicted. Data gathered by SOHO's MDI (Michelson Doppler Imager) and VIRGO (Variability of Solar Irradiance and Gravity Oscillations) instruments.