In June 2001, a Delta rocket started NASA’s 840-kg Microwave Anisotropy Probe (MAP) on a journey that, a few weeks later, brought it to the vicinity of the L2 Lagrange point, 1.5 million km antisunward of Earth. From that remote and unobstructed perch, the instrument has been continuously mapping, with unprecedented precision, the very faint departures from the almost perfect isotropy of the cosmic microwave background (see figure 1) and the still fainter polarization engendered by these anisotropies.

The much-anticipated report of MAP’s first full year of observation, detailed in 13 papers released on 11 February, 1 was accompanied by a ceremonial announcement. In memory of Princeton University astrophysicist David Wilkinson, a founding member of the MAP collaboration who died last September, the spacecraft had been rechristened the Wilkinson Microwave Anisotropy Probe (WMAP). Wilkinson had been a pioneer of cosmic microwave background (CMB) measurement since 1964.

WMAP was built...

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