The Sun

The Sun is a massive burning ball of gases held together by gravity. It is primarily composed of helium and hydrogen gases.

The Sun has three main layers—the core, the radiative zone and the convective zone. The Sun’s atmosphere is made up of the photosphere, chromosphere and corona.

The core at the center of the Sun produces the Sun’s heat. This energy is produced by hydrogen nuclear fusion reactions. During nuclear fusion, two or more protons fuse to form helium, and large amounts of energy are released.

Energy produced in the Sun’s core is carried to the Sun’s surface in the form of light energy called photons. This energy moves from the core into a very dense radiative zone. It can take thousands of years for the light energy to move through this layer and into the convective zone.

The outer layer of the Sun is called the convective zone. Hot gases in this layer rise toward the surface, where they become cooler and denser. The gases then descend back into the Sun. This circulating movement is called convection, and is similar to currents in the Earth’s mantle.

The photosphere is the inner layer of the Sun’s atmosphere. This gaseous layer is thick enough to be visible. When we look at the Sun, we are seeing the photosphere.

Just beyond the photosphere is a thin layer called the chromosphere, which has a reddish color. The chromosphere can be seen during a total solar eclipse when the Moon covers the Sun.

The outer atmosphere of the Sun is called the corona. It extends for millions of kilometers beyond the Sun, and is composed of gases. It can only be seen during a total solar eclipse.

Sunspots are cooler, darker areas of gas on the Sun’s surface. Cooler gases emit less light than hotter gases. These areas are caused by the Sun’s magnetic field affecting the convection heat. Scientists have discovered that the number of sunspots varies over an 11-year cycle.

Solar flares are enormous areas of extreme temperature on the Sun’s surface, caused by magnetic fields. Solar flares typically occur near sunspots. When a solar flare erupts, streams of charged gas particles extend thousands of kilometers into space.