COSMIC MICROWAVE BACKGROUND
13.7 billion light-years
The ultimate limit of our vision, the cosmic microwave background is the remnant of the Big Bang fireball in which the whole Universe was thought to be created. This image made by the WMAP satellite shows the whole sky unfolded onto a flat image, and is covered with tiny variations in temperature, shown by the different colours. These fluctuations are thought to be the structures that eventually formed into galaxies during the very early Universe.
Credit: Microwaves by the WMAP Science Team for NASA.
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