index A age of universe, 232­233 aliens. See extraterrestrial life Alpha Centauri (binary star system), 185, 205 ancient beliefs about universe, 18­19 Andromeda galaxy collision with Milky Way galaxy, 109 discovery as galaxy, 144­145 distance from Earth, 144 early observation of, 120 annihilation, 170 annual parallax, 126, 186­188 antimatter, 169­171 antiquarks, 169­171 aperture of telescopes, 121 Apollo space missions, 13, 67 Arecibo Message, 182 Aristarchus, 40­41, 45­47, 125 Aristotle, 39 Big Crunch, 226 black holes, 108­109 board game, Kaguya-go Journey, 206­207 bosons, 168 negative curvature, 221­222 positive curvature, 219­221 cylindrical-shaped space, 220­221 D dark energy, 109, 166, 227­228 dark matter, 109, 166, 226 de Sitter universe, 232 Democritus, 116, 120 density constant, 228 density of matter, average, 227­228 disc-shaped galactic model, 117­119 distances. See measuring distances Doppler effect, 147 Drake, Frank, 180­181, 184 Drake equation, 180­181 dynamic universe, 222­227 C Cannon, Annie Jump, 188 capture hypothesis, 93 celestial sphere, 19 Cepheid variable stars, 188­189 CfA2 Great Wall, 141 China, development of astronomy in, 19 closed universe, 222­223, 228, 230, 232 clusters of galaxies, 111 formation of, 173, 175 Local Group, 140­141, 207 mass of, 226 number of galaxies in, 140 e Earth