THE SUN
Our Sun is an ordinary star. Compared with other stars, it's not very large or very hot. Yet, from our perspective, the Sun is just the right size and temperature. If it were bigger, it would have exploded long ago. If it were smaller, it would not produce enough heat and light to sustain light on Earth.
The heat and light- or energy - is created in the Sun's core by nuclear fusion. Nuclear fusion creates an enormous release of tiny bits of energy called photons. It takes photons up to 10 million of years to reach the Sun's surface but only eight minutes to reach Earth. The sunlight you see everyday was created 10 million years ago.
The Sun's main layers are the solar core, radioactive zone, chromosphere, convection zone, photosphere, and corona.
The core of the Sun is a gigantic nuclear furnace. Each second, the core transforms 700 million tons of hydrogen gas into helium gas by nuclear fusion. The energy it produces each second is equal to 90 billion 1 megaton bombs going off each second. Each second, 5 million tons of matter are changed into energy.
The radioactive zone is the reason why it takes photons millions of years to reach the surface. As the photons rush out from the core, they pass through a thick layer of slightly cooler gas known as the radioactive zone. The photons bounce around like balls in a pinball game. Each photon can only travel a fraction of a centimeter before hitting an atom of gas and getting knocked back.
The chromosphere is the layer of the atmosphere where the solar fireworks take place. Fiery jets of gas called spicules leap to heights of 9,00 km (6,000 miles) and more, powerful flare explode. This is also where prominence begin to loop or erupt high above the Sun's surface.
In the convection zone, enormous bubbles of intensely hot gas shoot toward the Sun's surface, come back down, and does it all over again.
The photosphere is the Sun's surface. It's the layer we see from Earth. The reason we can see it is because the layers above it are transparent. The photosphere is covered by granules. Granules are small, bright bubbles caused by hot and cooler gases flowing just beneath the surface. They bring bring the Sun's energy to its surface.
The corona is the outermost layer of the Sun's atmosphere and is filled with super hott gases. It stretches for more than 1 million km (620,000 miles) into space and is always expanding and changing its shape.