The Milky Way is our own galaxy. The Sun is the closest star to Earth and the center of our solar system. The Sun weighs more than 300,000 times as much as Earth and is 109 times larger. Sunspots appear as dark spots on the Sun, and are believed to be cooler than the rest of the Sun. They appear in 11-year cycles.
Planet is the term used for a body in orbit around the Sun.
The first letter of each word is the first letter of each planet. Since 1994, evidence has been found that planets also exist beyond our solar system. At least 10 planets existing in other solar systems have been discovered. As long as our own Moon was the only moon known, there was no need for a general term for the moons of planets. Orbit is the term for the path traveled by a body in space.