An all-sky image from WMAP showing the extremely small variations in the Cosmic Microwave Background.  These variations help explain the "clumpy" structure of the present universe and measurements of the sizes and polarization of these variations allow us to determine other characteristics of the universe (see below).

Top graph shows peaks in the distribution of angular sizes of the CMB variations.  The large peak at approx. 1 degree indicates the universe must be very close to "flat" (see outline for space-time curvatures).

The bottom graph shows peaks in the distribution of the polarization of the CMB variations.  The point labeled "Reionization" indicates the first stars formed earlier than previously theorized.