Figure 17.2: The Hubble deep field. Perhaps no single picture is more convincing that we live in a universe of galaxies than this image from the Hubble space telescope. This image covers just a narrow region of the sky with an angular size 1/30 of that subtended by the full Moon. The region is so small that just a few foreground stars in our own galaxy are visible. However, the picture includes very faint objects whose light has been traveling to us a long time over great distances. The light from the most distant galaxies may have been emitted less than 1 billion years after the big bang---less than 6% of the present age.