The sun’s photosphere

The sun's photosphere

The photosphere is the visible surface of the Sun that we are most familiar with. Since the Sun is a ball of gas, this is not a solid surface but is actually a layer about 100 km thick (very, very, thin compared to the 700,000 km radius of the Sun). When we look at the center of the disk of the Sun we look straight in and see somewhat hotter and brighter regions. When we look at the limb, or edge, of the solar disk we see light that has taken a slanting path through this layer and we only see through the upper, cooler and dimmer regions. This explains the “limb darkening” that appears as a darkening of the solar disk near the limb.

A number of features can be observed in the photosphere with a simple telescope (along with a good filter to reduce the intensity of sunlight to safely observable levels). These features include the dark sunspots, the bright faculae, and granules. We can also measure the flow of material in the photosphere using the Doppler effect. These measurements reveal additional features such as supergranules as well as large scale flows and a pattern of waves and oscillations.
Image and caption courtesy of NASA/MSFC Solar Physics.