A star is a huge ball of hot, glowing gas that makes its own light — the Sun is our nearest star.
A galaxy is a vast group of stars; our galaxy is the Milky Way. The universe contains billions of galaxies. Distances in space are so large they are measured in light-years (the distance light travels in a year).
Remember
- Star → galaxy → universe (smallest to largest).
- A light-year is a distance, not a time.