Read the excerpt from Chapter Three of Windows to the Universe: Revolutions in Astronomy.One of Hubble's most famous images is the Hubble Deep Field, which reveals thousands of galaxies in a tiny part of the sky. By examining this image, scientists could see galaxies billions of light-years away, providing a glimpse of what the universe looked like in its early stages. The Hubble Space Telescope has helped answer many questions, but it has also created new mysteries about dark matter, dark energy, and the formation of galaxies.