After COBE, experimental cosmologists planned new and more precise measurements. The successor to COBE is the Microwave Anisotropy Project, now called the Wilkinson Microwave Anisotropy Project (WMAP) in honor of David Wilkinson, a leader on both COBE and MAP, who died in 2002.

Unlike COBE, whose orbit was a few hundred miles high, WMAP occupies an orbit about 1.5 million kilometers from Earth around the Lagrange point “L2,” as shown in the drawings. At Lagrange points, the combined effect of the gravity of the Earth and the sun enable a spacecraft to assume a stable orbit around a point in empty space. WMAP’s detector always points away from the sun and sweeps across the whole sky in one year. Note that the design of the probe includes a large circular shield to prevent sunlight from reaching the detector.

WMAP on its way to its orbit around the Lagrange point L2. From this orbit, the WMAP detector points outward approximately along the line between the sun and Earth. Note the circular baffle that prevents light from the sun from reaching the detector. (image courtesy of NASA/ WMAP science team)

The Lagrange points, with WMAP in orbit about L2. (image courtesy of NASA/WMAP science team)

A comparison in the imaging of the microwave background by COBE and WMAP. (image courtesy of NASA)

WMAP improved the temperature sensitivity by a factor of a thousand and the angular resolution—the fineness of detail—by a factor of 30. For comparison, two images, one above the other, show the whole-sky measurements for the microwave background for COBE and WMAP.

Key implications of the WMAP measurements include these:

• A more accurate age of the universe, 13.7 billion years, plus or minus .2 billion years
• A more accurate date for the beginning of star formation—only 200 million years after the Big Bang, three times sooner than previously thought.
• Evidence that the universe will expand forever
• More evidence for the inflation model

With WMAP, cosmology has achieved the status of “precision science,” a great advance for a field that wasn’t taken very seriously only fifty years ago. And cosmologists are already planning the next generation of microwave background probes.