Sun's structure. Composite image including SOHO (Solar and Heliospheric Observatory) satellite images of the Sun's structure. Nuclear radiation, produced in the core (white, centre), is re- radiated as light and heat in the radiative zone (yellow, upper centre). In the convective zone (orange, upper frame), heat passes to the surface, the photosphere (yellow, lower left). On this are sunspots (dark), areas of higher solar activity. The Sun's activity peaks every 10-11 years. Above the photosphere is the chromosphere (orange, lower centre), from which flares (white, lower right) and prominences (orange, top right) arise. The Sun's lower half is formed from SOHO images.