Grades 3–5 · Earth & Space
Why do dark spots appear on the bright Sun?
A sunspot looks dark when compared with the bright surface around it. It is not a cold hole or a patch of ordinary dirt. Sunspots are regions that remain extremely hot but are cooler than nearby areas.
In the diagramA cooler region appears darker by contrastusual heat transportstrong magnetic regionless light from a still extremely hot patchOnly a schematic: never view the Sun without protection.
The Sun contains moving electrically charged gas. This motion is connected with magnetic fields. Where magnetic fields become especially strong, they can interfere with the usual movement carrying heat toward the visible surface.
The affected region receives less heat from below and emits less light than its surroundings. That contrast makes the spot appear dark in an image. Viewed by itself, such hot material would still be very bright.
Sunspots change as solar magnetic activity changes. Scientists use their numbers and patterns as clues about that activity. The marks are temporary features of a changing star, rather than permanent continents on a solid surface.
About this explanation
Starting knowledge: Know that hotter glowing surfaces can emit more light and that the Sun has magnetic activity.
Sources
- NASA Space Place — Sunspots and Solar Flares