Sunspots appear dark because they are cooler than the surrounding areas on the Sun's surface. While the surface of the Sun, or the photosphere, typically has a temperature around 5,500 degrees Celsius (about 10,000 degrees Fahrenheit), sunspots have a lower temperature—around 3,500 degrees Celsius (about 6,300 degrees Fahrenheit). This temperature difference means sunspots emit less light, making them look dark in contrast to the much hotter and brighter surroundings. However, sunspots are not truly black; if isolated, they would still be very bright, about as bright as the full moon as seen from Earth. The lower temperature is caused by intense magnetic fields in sunspots, which inhibit the flow of heat from the Sun's interior to its surface, leading to cooler, darker regions.
In summary, sunspots are dark visually due to the contrast in temperature and brightness with the surrounding hotter solar surface, and the strong magnetic fields are the reason these areas cool down.
