There Are No Green Stars
When astrophysicists peer into the universe, they see a nearly perfect rainbow spectrum of stars, from cooler red ones on one side to hotter blue ones on the other. In the center of the spectrum, they should see green stars, but they don’t due to the nature of stars and the limitations of the human eye.
Let There Be Light
A star begins its life as a cloud of hydrogen gas. Due to gravity, the cloud condenses. If the cloud is big enough, it will have enough gravity to create the temperature and pressure needed in its core to fuse hydrogen together ( along with the help of quantum tunneling). The original hydrogen atoms have slightly more mass than the helium they fuse into, and this missing mass is converted into energy, as shown by Einstein’s E=mc^2. Small amounts of mass (m) are converted into incredible amounts of energy (E) when multiplied by the speed of light squared (c^2), about 9 x 10 16m^2/s^2. This is what generates the majority of light from stars, although bigger stars can fuse helium into heavier elements and these heavier elements into even heavier ones, all of which releases energy, until it tries to fuse iron, causing a supernova event.
