Which darkened area of a sunspot is a?

The darkened area of a sunspot is called the umbra. It appears darker than the surrounding areas because it is cooler, with temperatures around 3,000 to 4,000 degrees Celsius, compared to the Sun's surface temperature of about 5,500 degrees Celsius. Surrounding the umbra is the penumbra, which is lighter and partially shaded, where temperatures are slightly higher. Sunspots are temporary phenomena caused by magnetic activity on the Sun's surface.