The Sun's interior is very hot. Its inner most part is called the core and it is a mass made up of glowing gas that produces energy. The core gives off a large amount of energy including all the Sun's light and heat. The Sun's mass is made up mostly of hydrogen, which is three times the amount of helium, and very small amounts of other chemical elements. In the core temperature and pressure are so tremendous that nuclear fusion causes hydrogen atoms to join together to form helium. The temperature inside the Sun core is about 15 million degrees Celsius.(1) The total mass of the helium produced by nuclear fusion is slightly less than the total mass of the hydrogen that goes into it. The change in mass occurs because some of the matter is converted into light and heat energy. The light and heat energy slowly move from the core of the Sun to its atmosphere and escape into space.
The Sun transports heat by two ways. The inner layer (center to 7/10 of the way out) is radiative. In the radiative zone, energy from the core slowly travels outward by the movement of radiation. This zone is so dense that the Sun's energy takes about 150,000 years to work its way through. The convection zone (the outer 3/10th up) has rising and falling plumes and materials that carry energy from the radiative zone to the surface. Some of this energy reaching the Earth energy is its main source of energy. There is enough hydrogen fuel in the core of the Sun to last for a total of 10 billion years and the Sun is now only about 5 billion years old.(2)
The Sun's Atmosphere
The Sun's atmosphere has three layers: 1) the photosphere, 2) the chromosphere, and 3) the corona. There are no sharp boundaries between the layers of the Sun.
The word photosphere comes from a Greek word with "photo" meaning light, so photosphere means the sphere that makes light.
The photosphere is a visible outer layer of the Sun's atmosphere. In the photosphere, energy escapes from the interior and streams into the Sun's atmosphere and beyond. Sunspots are located in the photosphere. Sunspots are dark blemishes on the Sun's surface. They appear dark because they are much cooler than the area around them. Solar flares occur sometimes from the large sunspots. Solar flares are violent eruptive events on the Sun. These eruptions may cause a large quantity of particles and radiation to blast out into space. The eruptions can also cause disturbances that spread outward in the solar atmosphere. The energy from a solar flare is released from the intense magnetic field around a sunspot group.(3)
The word chromosphere comes from a Greek word chromo that means, 'color', so the chromosphere is the color sphere. It is the middle layer of the Sun's atmosphere located above the photosphere. It has great looping arcs of hot gases called prominences that erupt from the Sun. If you have ever seen the end of a total eclipse of the Sun, you can see a reddish glow just around the photosphere. Chromosphere has intense explosions gives off large amount of energy called solar flares that enter into space.
The corona is the outer layer, which looks like a white halo around the Sun, can be seen during an eclipse. Corona means crown in Latin. The corona is the Sun's extended outer atmosphere. It sends out a stream of electrically charged particles called solar wind. The corona is much hotter than the surface of the Sun. It is so hot that it produces high energy light called X-rays. The corona is so hot, but it won't feel hot because it is not very dense. The corona contains very little thermal energy. The reason is that it is like a vacuum. Because of the corona's high temperature, the atoms there are moving at very high speeds. But because there are so few moving atoms in the corona, the total amount of energy these moving atoms have is low.(4)
Since the Earth's climate system is driven by energy from the Sun, the next section will discuss whether a brighter Sun is also responsible for rising temperatures.