A smaller star, like the Sun, will gradually cool down and stop glowing. During these changes, it will go through the planetary nebula phase and white dwarf phase. After many thousands of millions of years, it will stop glowing and become a black dwarf. A massive star experiences a much more energetic and violent end. What determines the route a star takes, it depends on its mass and composition. Stars are form by large clouds of dust and gas from a nebulae. The route the sun takes through its life cycle is characterized by its main sequence.

A galaxy is a massive, gravitationally bound system of stars, stellar remnants, interstellar gas, dust, and dark matter. We classify galaxies by studying its appearance, the arm tightness, and presence of the bars. The three main types of galaxies are Spiral, Elliptical, and Irregular. Spiral is characterized by a flat disk, central bulge, and arms with young stars. Elliptical is a smooth, oval/spherical with mostly old stars and little gas. Irregular lacks a structure, often chaotic, with mixed star ages and active stars.