Answer

We see planets in visible light because they reflect Sunlight. They act as mirrors for the Sun. A star is defined by having nuclear fusion to power it, this is what makes the Sun so hot that it radiates most of its light in visible wavelengths. Our Sun is really just one big hydrogen bomb. In the core of our Sun, two hydrogen atoms are forced together to make another element, helium. When the hydrogens are forced together, a huge amount of energy is released. This is what powers the Sun.