Figure 14-5 RIVUXG Spiral Galaxies Edwin Hubble classified spiral galaxies according to the size of their central bulges and the appearance of their arms. At one end of the range, (a) Sa galaxies have the largest and most obvious central bulges and tightly wrapped, smooth, broad spiral arms, while (b) Sb galaxies are more moderate, and (c) Sc galaxies have the smallest central bulges with loosely wrapped arms. (a: Adam Block/Steve Mandel/Jim Rada and Students/NOAO/AURA/NSF; b: NASA/JPL-Caltech/ESA/Harvard-Smithsonian CfA; c: FORS Team, 8.2-meter VLT, ESO)