Which object has the oldest light we can directly observe?

The cosmic microwave background, or CMB, is the oldest electromagnetic radiation observable from the universe. It was emitted when the universe cooled enough for neutral atoms to form, roughly 380,000 years after the Big Bang. Before that, the universe was opaque to light because electrons and nuclei were not yet bound into atoms. The CMB was first detected in 1965 by Arno Penzias and Robert Wilson. Later missions such as COBE, WMAP, and Planck mapped it with increasing precision, revealing the early structure of the cosmos.