Lesson 3

3

Our Galaxy

Why does everything in space seem to spin and swirl together?

Earth belongs to a solar system within the Milky Way, one of billions of galaxies. This lesson covers how galaxies and solar systems are organized and where Earth fits within those larger structures.

Click here to hear the lesson video

Key Ideas

  • We live in a galaxy called the Milky Way, made of hundreds of billions of stars, gas, and dust.
  • The Milky Way is a spiral galaxy, and our solar system orbits within one of its arms.
  • Our solar system formed from a cloud of gas and dust pulled together by gravity.
  • The Sun sits at the center; 8 planets orbit around it, including Earth.
  • There are billions of galaxies in the universe. The Milky Way is just one of them.

Spines

  • DK's Science as You've Never Seen it Befor
    • Galaxies pg. 114-115 
    • The Solar System pg. 120-121
  • Mammoth Science: Solar System pg. 152, Milky Way pg. 154
  • Visual Timelines: Life on Earth pg. 10
  • Alternative: NASA’s Space Place (https://spaceplace.nasa.gov/menu/space/) (explore the website)

Vocabulary

  • Galaxy: A huge collection of stars, gas, dust, and dark matter held together by gravity; our galaxy is the Milky Way.
  • Solar System: Our Sun and everything that orbits it: eight planets, moons, asteroids, comets, and other objects.
  • Orbit: The curved path one object takes around another due to gravity, like Earth's path around the Sun.
  • Planet: A large, round object that orbits a star and has cleared the space around its orbit.

Discussion Questions

  1. What is the name of the galaxy we live in?
    Sample Answer: We live in the Milky Way.
  2. What kinds of things are found in the Milky Way?
    Sample Answer: The Milky Way has stars, planets, gas, and dust.
  3. How is a galaxy different from a solar system?
    Sample Answer: A solar system has one star and its planets, but a galaxy has billions of stars and many solar systems.
  4. Where is our solar system inside the Milky Way?
    Sample Answer: Our solar system is in one of the spiral arms of the Milky Way.

Digging Deeper

  1. How do scientists prove something exists if they can't see it? Vera Rubin couldn't see dark matter, but she could see what it was doing. Research how scientists use indirect evidence to prove something exists. Think about dark matter, and then think about the Big Bang. Neither can be directly observed. What evidence points to each one?
    Sample Answer: Scientists look for indirect evidence, which means the effects something has on things we can see. Vera Rubin could not see dark matter, but she could see what it was doing to how galaxies spin.
  2. How is this similar to or different from how a detective solves a crime?
    Sample Answer: Answers will vary.