Just like Earth, the sun boasts it own atmosphere, which is composed of the photosphere, the chromosphere and the corona.
This is the lowest region of the sun's atmosphere and the area that we can see. The surface of the sun typically refers to the photosphere, at least in lay terms. It is 180 to 240 miles (around 290 to 390 km wide) and between 4,000 and 6,000 degrees Kelvin (from the top to the bottom).
It appears granulated or bubbly, much like the surface of a simmering pot of water. The bumps are the upper surfaces of the convection current cells beneath; each granulation can be 600 miles (1,000 km) wide.
As we pass up through the photosphere, the temperature drops and the gases, because they are cooler, do not emit as much light energy. This makes them less opaque to the human eye. Therefore, the outer edge of the photosphere looks dark due to an effect called limb darkening that accounts for the clear crisp edge of the sun's surface.
The area extends above the photosphere to about 1,200 miles (2,000 kilometers). The temperature rises across the chromosphere from 4,500 degrees Kelvin to about 10,000 degrees Kelvin. The chromosphere is thought to be heated by convection within the underlying photosphere.
As gases churn in the photosphere, they produce shock waves that heat the surrounding gas and send it piercing through the chromosphere in millions of tiny spikes of hot gas called spicules.
Each spicule rises to approximately 3,000 miles (5,000 kilometers) above the photosphere and lasts only a few minutes. Spicules may also follow along magnetic field lines of the sun, which are made by the movements of gases from the solar interior.
This final layer of the sun extends several million miles or kilometers outward from the other spheres. The corona can be seen best during a solar eclipse and in X-ray images of the sun. The temperature of the corona averages 2 million degrees Kelvin.
Although no one is sure why the corona is so hot, it is thought to be caused by the sun's magnetism. The corona has bright areas (hot) and dark areas called coronal holes. Coronal holes are relatively cool and thought to be areas where particles of the solar wind escape.