The discovery of the Cosmic Microwave Background is regarded as one of the most important of all science, as it is relic radiation from its early hot, dense epochs. We see that it was a key prediction of the Big Bang, which was discovered by accident by Penzias and Wilson. By studying the microwave sky in detail, the COBE, WMAP and Planck probes of NASA and ESA have shown us that the CMB is a perfect blackbody, meaning it’s all at the same temperature, 2.7 Kelvin. When we study the tiny fluctuations and anisotropies away from this near-perfect spectrum, we find that we can learn what the universe was like when it was roughly 350,000 years old. We learn the conditions that created the CMB, as we watch atoms combine together for the first time, letting light slip free to come to us 13.6 billion years later. This observation alone is proof of the Big Bang. This is part of my complete intro Astronomy class that I taught at Willam Paterson University and CUNY Hunter.

NASA's Cosmic Background Explorer (COBE): https://science.nasa.gov/missions/cobe
NASA's Wilkinson Microwave Anisotropy Probe: https://map.gsfc.nasa.gov/universe/
ESA's Planck Mission: https://www.esa.int/Our_Activities/Sp...