11. During which missions did humans first walk on the Moon? a. Mariner 4 b. Saturn V c. Apollo 11 d. Apollo 13 12. Define the following: a. Star b. Asteroid c. Comet d. Meteorite e. Satellite

11. **c. Apollo 11**<br /><br />12. Definitions:<br /><br />* **a. Star:** A massive, luminous sphere of plasma held together by its own gravity. Stars produce energy through nuclear fusion in their cores, converting hydrogen into helium and releasing vast amounts of light and heat.<br /><br />* **b. Asteroid:** A small, rocky body orbiting the Sun. Most asteroids are found in the asteroid belt, a region between the orbits of Mars and Jupiter.<br /><br />* **c. Comet:** A small, icy body orbiting the Sun. When a comet approaches the Sun, its ices sublimate (turn directly from solid to gas), forming a coma (a cloud of gas and dust around the nucleus) and often a tail or two.<br /><br />* **d. Meteorite:** A small piece of rock or metal from space that survives its passage through the Earth's atmosphere and lands on the Earth's surface. It is a meteoroid that has reached the ground.<br /><br />* **e. Satellite:** An object that orbits a planet, dwarf planet, or other larger celestial body. Satellites can be natural (like the Moon orbiting Earth) or artificial (like the International Space Station orbiting Earth).<br />