- Objects we observe in the sky are called heavenly bodies or celestial bodies.
- Celestial bodies include stars, planets, satellites, asteroids, comets, and meteors.
- The universe originated around 2000 crore years ago from a singularity, due to the Big Bang.
- The Big Bang theory explains the expansion of the universe from a hot, dense state to its current state of vastness and relative coolness.
- A galaxy is a huge system of billions of stars, dust, and gases. There are millions of galaxies in the universe .
- Sun and all the other stars that we observed in the night belong to a Milky Way galaxy or Akash Ganga.