Arno Penzias and Robert Wilson discovered cosmic microwave background radiation (CMBR) in 1964, for which they received the Nobel Prize in 1978. CMBR provides evidence of a primordial hot, dense phase early in the universe called the singularity. The Cosmic Background Explorer satellite (COBE), launched in 1989, mapped the CMBR, showing it is nearly uniform in all directions with slight temperature fluctuations that gave rise to all subsequent structure in the universe.