Observing sunspots drift across the surface helped astronomers discover that the Sun actually rotates on its axis – the polar regions take longer to complete a rotation than the equatorial regions because the Sun isn’t solid. Sunspots are generally surrounded by lighter areas called faculae. Sunspots, indicators of disturbed magnetic fields, are the most common features seen in the photosphere. There is some variation in temperature from place to place within the photosphere – for example, sunspots are relatively “cool” regions with temperatures as low as 3,000 ☌ (5,400 ☏). Surprisingly, the photosphere is also much cooler than the atmosphere above it, which has regions with temperatures as hot as 2 million ☌ (3.5 million ☏). Instead, energy radiates away through space, some of it reaching Earth. Because the plasma is cooler and less dense at the surface, there are fewer collisions to trap the energy carrying photons within the Sun. Most of the light energy produced in the Sun’s core escapes from the photosphere. The temperature of the photosphere is around 5,500 ☌ (9,900 ☏), which is much cooler than the Sun's core. It is only about 500 km (300 miles) wide, a much thinner layer than the interior solar regions. The photosphere is a thinner, cooler layer than its neighboring layers. The Photosphere is Cooler Than the Layers Around It The surface of the Sun is the only part that we can see from Earth on a typical day, without use of specialized equipment. The surface of the Sun is called the photosphere, a term which means “sphere of light.” The glowing ball of light that you see in the sky is the photosphere. Though the visible light emitted by the Sun is actually white light, we often perceive sunlight as yellow due to scattering of shorter, blue wavelengths as light passes through the atmosphere. This color enhanced view of the Sun shows sunspots on the surface, or photosphere, of the Sun.
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