+ Visit NASA.gov + Advanced Search   + About the Server   + Animation List   + How to Use the Server   + RSS Feeds Previous Animation Next Animation The Cosmic Dawn (Still Image w/o Titles) About 300,000 years after the Big Bang, the Universe spread out enough that free electrons and protons could form atomic hydrogen. These atoms readily absorb light, thus creating an opaque murky era known as the cosmic Dark Ages. Roughly 900 million years later, the Universe underwent a Reionization Period. The earliest stars and quasars generated enough ultraviolet light to turn hydrogen atoms back into protons and electrons. These areas began as bubbles, continually spreading until light was permitted to travel freely through the Universe. This moment has been dubbed the Cosmic Dawn.    This still image shows the timeline running from the Big Bang on the right, towards the present on the left. In the middle is the Reionization Period, when the initial bubbles caused the Cosmic Dawn. Available formats:   1280 x 720       TIFF 2 MB   320 x 180         PNG 219 KB   160 x 80           PNG 52 KB   80 x 40             PNG 13 KB Animation Number: 10131 Completed: 2006-10-01 Goddard TV Tape: G2007-007HD Keywords: SVS >> HDTV SVS >> Astrophysics SVS >> Early Universe SVS >> Cosmology SVS >> Big Bang SVS >> Universe     Please give credit for this item to NASA/STScI Back to Top + Privacy Policy and Important Notices + Reproduction Guidelines NASA Official: SVS Contact: Curator: