1. NUCLEAR FUSION

2. Stars shine because of nuclear fusion
Stars shine because of nuclear fusion. Fusion reactions in the Sun's core keep our nearest star burning. Stars are made mostly of hydrogen and helium(lightweight gases) A star contains so much hydrogen and helium that the weight of these gases is enormous. The pressure at the center of a star is great enough to heat the gases. This causes nuclear fusion reactions.

3. We call it nuclear fusion because at extreme temperatures of millions of degrees, the collision of atomic nuclei (center) causes the atoms to fuse (join) together.

4. In stars like our Sun, two hydrogen atoms join together to create a helium atom. Nuclear fusion reactions need a lot of energy to get started. Once they begin, they produce even more energy.

5. The sun’s energy comes from fusion in its core, where temperatures reach millions of Kelvin. Hydrogen fuses into helium (in all stars). Helium fuses into heavier elements (in high- mass stars).

6. Nuclear fusion of hydrogen, to form helium occurs naturally in the sun and other stars. It takes place only at extremely high temperatures. A great deal of energy is needed to overcome the force of repulsion between positively charged nuclei.

7. NUCLEAR FISSION

8. Nuclear fusion is the opposite of nuclear fission
Nuclear fusion is the opposite of nuclear fission. When a nucleus fissions, it splits into several smaller fragments. These fragments, or fission products, are about equal to half the original mass. Two or three neutrons are also emitted.

9. The sum of the masses of these fragments is less
The sum of the masses of these fragments is less than the original mass.
This 'missing' mass (about 0.1 percent of the original mass) has been converted into energy according to Einstein's equation.
Fission can occur when a nucleus of a heavy atom captures a neutron, or it can happen spontaneously.