June 1963: Discovery of the Cosmic Microwave Background.

How was CMB discovered?

But the CMB was first found by accident. In 1965, two researchers with Bell Telephone Laboratories (Arno Penzias and Robert Wilson) were creating a radio receiver, and were puzzled by the noise it was picking up. ... Dicke's team got wind of the Bell experiment and realized the CMB had been found.

When was CMB emitted?

The CMB radiation was emitted 13.7 billion years ago, only a few hundred thousand years after the Big Bang, long before stars or galaxies ever existed.