WMAP Cosmology

The mission

WMAP launched in June 2001 and spent nine years observing the cosmic microwave background from a stable orbit around the Sun-Earth L2 point, a million miles from Earth. By measuring tiny differences in the temperature of the oldest light, millionths of a kelvin across the sky, it turned the CMB into a precision tool for cosmology.

WMAP followed the COBE mission, which first detected those large-scale ripples, and improved the measurement dramatically. Its nine-year dataset, released in 2012, set the benchmark that the later Planck satellite refined still further.

What it measured

• The CMB temperature map: the pattern of hot and cold spots that records conditions 380,000 years after the Big Bang.
• The CMB's polarisation: a signature of the reionization era, when the first stars lit up the universe.
• The age and recipe: enough precision to pin down how old the universe is and what it is made of.

The cosmic recipe

From WMAP's nine-year results, the universe is about 13.77 billion years old. By energy, it is roughly 4.6% ordinary atoms, about 24% dark matter, and about 71% dark energy, a value later refined by Planck. In other words, almost everything in the universe is dark and still poorly understood.

Universe 101

WMAP's Universe 101 guide is NASA's plain-language introduction to the Big Bang, the expansion of space, the cosmic microwave background, and dark matter and dark energy. It is built around the results WMAP helped establish, and it remains one of the clearest starting points in cosmology.