Image credits
Image Credits:

Photos: Milky Way Galaxy Milky Way as seen from Earth: courtesy of Photo Researchers; Q&A with Astronomer Julianne Dalcanton:Julianne Dalcanton: courtesy of Julianne Dalcanton; Spiral galaxy: courtesy of AURA/NOAO/NSF; Elliptical galaxy: courtesy of STScI; Irregular Galaxy: courtesy of Bill Shoening/AURA/NOAO/NSF; Sombrero Galaxy: courtesy of Bill Keel; Illustrations: How Much is a Billion: Jim Steck Q&A with Astronomer Julianne Dalcanton Amanda Duffy