1. HOMEWORK: PAGE 381 # 1, 5, 7, 8 9.3 UNSOLVED MYSTERIES

2. KEY CONCEPTS: The motions of stars and galaxies within clusters indicate that there are huge amounts of unseen matter, called dark matter, around each galaxy. Dark matter makes up about 23% of the universe- nearly 6 times more than visible matter. Dark energy makes up about 73 % of the universe. Astronomers believe that dark energy is responsible for the increased expansion of the universe

4. DARK MATTER AND DARK ENERGY Dark Matter: An undetected form of mass that emits little or no photons, but we know it must exist because we observe the effects of its gravity Dark Energy: An unknown form of energy that is causing the universe to expand faster over time

5. WHAT IS THE UNIVERSE MADE OF? Normal” Matter: ~ 4% Normal Matter inside stars:~ 0.6% Normal Matter outside stars:~ 3.4% Dark Matter: ~ 23% Dark Energy~ 73%