 As we observe the space around us, we see our solar system, our galaxy, and our local group of galaxies first. We then see significant numbers of large, well-formed galaxies in our local supercluster. The further out we see, the further back in time we go, and the further back in time we go, the more we notice a reduction in the size and structure of the galaxies. Eventually, we reach as far as the first galaxies to ever form from the first stars that started to shine. Before that was just hydrogen and dark matter. No light was being created for us to see. As we look back in time, we are also looking back at an ever-shrinking volume because the universe was getting smaller, and its temperature was getting hotter. Eventually it reached 3,000 degrees. At that point, hydrogen atoms began to disassociate into protons and electrons, and space became opaque. Coming back the other way, the surface, with the transition from opaque to transparent occurred, is called the surface of last scattering. At that time, all the photons in the universe were released. These photons are still with us today. We see them all across the sky in tremendous numbers. They are the cosmic microwave background photons, CMB, and they tell us a great deal about the past, present, and future of the universe.