We know that some stars exist because we can see them with our own eyes. In this lecture Walter Lewin provides illuminating evidence of stars we cannot see. He describes the birth of stars, in the arms of a nebula, to their explosive or implosive ends. There are super hot white dwarves, detectible only by measuring the shift in color as light leaves them. As some massive stars age, they collapse into incredibly dense neutron stars—1000 times smaller than white dwarves—that release more x-rays than light. One teaspoon of neutron star matter would weight 500 million tons. Lewin champions Jocelyn Bell, who discovered evidence for these stars in 1967 but was overlooked for the Nobel Prize. When Bell’s radio telescope picked up mysterious signals pulsing every 1.3 seconds, her lab described the phenomenon as “little green men,” at first unsure if these might be signs of intelligent alien life. In his ringing finale, Lewin pulls out a tuning fork to demonstrate the Doppler Effect, where the pitch of a sound changes as it moves. Astronomers measured an analogous Doppler shift in star light to prove the existence of black holes.