Image of the photosphere from the High Altitude Observatory. However, these sunspots are the site of strong magnetic fields. The solar magnetic field is believed to drive the complex activity seen on the Sun. Magnetographs measure the solar magnetic field at the photosphere. The bubbles of hot material welling up from below are seen at the photosphere, as slightly brighter regions.
Darker regions occur where cooler plasma is sinking to the interior.
This constantly churning pattern of convection is called the solar granulation pattern. Image of the photosphere from the High Altitude Observatory. All Rights Reserved.