What explains why sunspots appear darker than their surroundings?

Sunspots appear darker than their surroundings because they are regions with lower temperatures compared to the adjacent areas of the sun's surface, known as the photosphere. When sunspots form, they cool down to a temperature that is approximately 1000 to 1500 degrees Celsius cooler than the surrounding photosphere, which can be around 5500 degrees Celsius. This drop in temperature leads to a reduction in the amount of light emitted from these areas.

Since the photosphere is hotter, it emits more light and appears brighter, which makes the cooler sunspots appear darker. Thus, the contrast between the temperature of the sunspots and the hotter surrounding areas causes them to look dark against the bright backdrop of the sun. This phenomenon is crucial for understanding solar activity, as sunspots can affect solar radiation and, consequently, space weather.