- The sun, like others stars, is a ball of gas. In terms of the number of atoms, it is made of 91.0% hydrogen and 8.9% helium. By mass, the sun is about 70.6% hydrogen and 27.4% helium.
- The sun's enormous mass is held together by gravitational attraction, producing immense pressure and temperature at its core. The sun has six regions: the core, the radiative zone, and the convective zone in the interior; the visible surface, called the photosphere; the chromosphere; and the outermost region, the corona.
- At the core, the temperature is about 27 million degrees Fahrenheit (15 million degrees Celsius), which is sufficient to sustain thermonuclear fusion. This is a process in which atoms combine to form larger atoms and in the process release staggering amounts of energy. Specifically, in the sun's core, hydrogen atoms fuse to make helium.
- The energy produced in the core powers the sun and produces all the heat and light the sun emits. Energy from the core is carried outward by radiation, which bounces around the radiative zone, taking about 170,000 years to get from the core to the top of the convective zone. The temperature drops below 3.5 million degrees Fahrenheit (2 million degrees Celsius) in the convective zone, where large bubbles of hot plasma (a soup of ionized atoms) move upwards. The surface of the sun — the part we can see — is about 10,000 degrees Fahrenheit (5,500 degrees Celsius). That's much cooler than the blazing core, but it's still hot enough to make carbon, like diamonds and graphite, not just melt, but boil.
- The surface of the sun, the photosphere, is a 300-mile-thick (500-kilometer-thick) region, from which most of the sun's radiation escapes outward. This is not a solid surface like the surfaces of planets. Instead, this is the outer layer of the gassy star.
- We see radiation from the photosphere as sunlight when it reaches Earth about eight minutes after it leaves the sun. The temperature of the photosphere is about 10,000 degrees Fahrenheit (5,500 degrees Celsius).