1) Astronomy provides scientific, technological, philosophical, and practical benefits. It helps us understand our place in the universe. 2) The universe exists on immense scales that require special units of measurement like astronomical units and light-years. 3) The solar system includes the sun and planets, along with asteroids, comets, and other objects. Beyond our solar system are other stars, nebulae, galaxies, and more.

3. Astronomical distances and sizes are so large that astronomers use special units Astronomical Unit (AU) – applicable inside the solar system = average distance between Sun and Earth = 150,000,000 km = 1.5 x 10 8 km Light-Year (ly) – applicable between stars and galaxies = distance light travels in one year = ~ 9 x 10 12 km

11. Graphical Summary of the scale levels of the Universe, from the Earth, to the Solar System, to the Galaxy, to the Universe as a whole! Powers of Ten movie