The Sun is in fact a star, and a rather unremarkable one at that. It is of average size and is categorized as a yellow dwarf. It is composed of six layers or parts: the inner core, radiative zone, convection zone, photosphere, chromosphere, and corona. The first three form the interior; the next three constitute the solar atmosphere.
Inner Core: The inner core is the center of the Sun. It is where nuclear fusion takes place and where the energy of the Sun comes from. Despite its density the Sun is gaseous throughout because the high temperature gives the atoms so much energy of motion that they are unable of bond with one another to form a liquid or solid substance.
Radiative Zone: This section of the Sun is the largest part of the Sun, and includes the core. Energy travels in this zone through radiation. This layer is the inner 70% of the Sun. through here on its way to the top layer. Light from the core moves through the radiative zone as photons. Because the gas is so dense there the photon moves extremely slowly. It will go less than an inch before it is reabsorbed by an atom. It will then be reemitted but will soon be reabsorbed. This constant absorption and readmission slows down the photons like cars in stop and go traffic. It will take almost a million years for a photon to reach the surface.(12)
Convection Zone: This area carries the energy up to the surface. It comprises the outer 30% of the Sun. The gas warms up and rises and then cools and sinks back. Scientists know this because of granulation which occurs at the surface when hotter gases emerge among the cooler gas at the surface. The gas then releases its heat into space and returns down to continue the convection process.
Photosphere: This is the part of the Sun that we can see. It is the surface of the Sun but we couldn't stand on it – it is made of gases. The sunlight emanates from this thin layer thus giving the illusion that it has a hard surface. Because of its high internal temperature the Sun is gaseous throughout its volume.
Chromosphere: This layer of gas above the photosphere can only be seen with the help of a special telescope. This layer of gas has much lower density than that of the photosphere. Its temperature reaches about 4500K at the bottom of the chromosphere and increases to about 25000K at the top.(13)
Corona: This is the outermost layer of the Sun which is usually only seen in photos taken during solar eclipses. It is very thin and faint. However, the temperature shoots up in the corona to around a million degrees Kelvin which is contrary to what one expects.
Solar Wind: While the Earth's gravity keeps the atmosphere from escaping the Sun's corona has such high temperatures that some of the gas does escape. This flowing gas is called the solar wind. Every second about a million tons of material is ejected by the Sun into the solar wind. Still with its large mass the Sun will eject only a few tenths of a percent of its total mass during its lifetime.
Granules: These are light colored regions with darker boundaries that are about 1000km (600miles) wide.(14) The photosphere is covered with this pattern blotchy pattern. The pattern is a result of the convection process. The rising hot gas gives off the lighter color but as the gas cools it moves out toward the boundary and sinks giving off the darker shade. This process is a continuous one.
Sunspots: These are not permanent features of the photosphere but occur in an 11-year cycle. When sunspots occur in large numbers the sun is said to be in an active stage. Sunspots are irregularly shaped dark regions in the photosphere. They vary greatly in size although most common ones are a few tens of thousands of kilometers wide. Sunspots can last from a few hours to a few months. Each sunspot has a dark center core called the umbra and a less dark border called the penumbra. A sunspot is a region where the temperature is relatively low which is why it appears darker than the surrounding area. Typically the umbra is about 4300K while the penumbra's temperature is around 5000K. This is quite a bit lower than the typical temperature of the photosphere is 5800K.(15)
Prominences: These are filaments that are appearing with the darkness of space behind them. They appear as bright arching columns of gas. They can go tens of thousands of miles above the photosphere. They can last for a few hours to a few months.
Solar Flares: These eruptions occur within a group of sunspots. The temperature rises quickly and a huge amount of particles and radiation are tossed into space. These eruptions can cause disturbances that spread out into the solar atmosphere.
Coronal Mass Ejections: When these eruptions occur they are more massive than the solar flares. More than a billion tons of high temperature gas is blasted into space at speeds of hundreds of thousands of kilometers per second.
If solar flares or coronal mass ejections happen to be aimed toward the Earth, the stream of material can reach us in a few days. When it reaches the earth it can interfere with satellites, and disrupt electrical and communications equipment.