86. The Sun, Stars & The Universe

This video explains the hierarchical organization of the universe, from local satellites to the vastness of the cosmos, and how we measure these immense distances.

1. Satellites and Star Systems

  • Satellites: Anything that orbits a planet.

    • Natural Satellites: Non-man-made objects like our Moon.

    • Artificial Satellites: Man-made objects used for communication or observation (e.g., orbiting telescopes).

  • Solar System: Refers specifically to our Sun and its eight planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune).

  • Star Systems: The general term for any other star and its surrounding planets.

  • Asteroids vs. Comets: * Asteroids: Made of rock and metal; mostly found in the belt between Mars and Jupiter.

    • Comets: Made of ice and dust; have highly elliptical orbits that reach the outskirts of the solar system.

2. Galaxies and the Universe

  • Galaxies: Massive collections of billions of stars held together by gravity. Our solar system is a tiny speck in the Milky Way galaxy.

  • The Universe: A vast expanse scattered with billions of galaxies. It is mostly empty space with unimaginable distances between them.

3. Measuring Distance: The Light Year

Because distances in space are too large for kilometers or miles, we use the Light Year.

  • Definition: The distance light travels in one year (approximately 9.5 trillion kilometers).

  • Speed of Light: Light travels at a constant speed of about 300,000 km/s.

  • Time as Distance: Because light takes time to travel, looking at distant stars is like looking back in time.

    • Proxima Centauri: Our next closest star is 4.24 light years away.

    • Polaris (North Star): About 433 light years away; the light we see from it today left the star over 400 years ago.

4. Summary Hierarchy

  1. Universe (The largest; contains all galaxies)

  2. Galaxies (Collections of billions of star systems)

  3. Star Systems / Solar System (A central star orbited by planets)

  4. Planets (Orbited by natural or artificial satellites)