2nd Part

Stars: The Building Blocks of Galaxies

A star is a massive, luminous ball of plasma, held together by its own gravity. The most important thing to know about stars is that they are powered by nuclear fusion. Deep in their core, incredible heat and pressure cause hydrogen atoms to fuse together to form helium, releasing a tremendous amount of energy in the process. This energy is what makes stars shine so brightly.

The color of a star tells you about its temperature. Hotter stars tend to appear blue or white, while cooler ones look yellow, orange, or even red. Our Sun is a yellow dwarf star.

Stars also have a life cycle, beginning their lives in massive clouds of gas and dust called nebulae. After a long life on the main sequence (like our Sun is now), a star will eventually die, becoming a white dwarf, a neutron star, or in the case of a very massive star, a black hole.