WMAP takes image of the universe. It takes images of Mars, Jupiter, and Saturn whose light takes about an hour to reach earth. Then it looks towards Andromeda, the next nearest galaxy from which light takes 2.3 millions year to reach earth. So we are looking 2.3 million years back into time. Thus it moves on to seek light from more distant area to discover the past and finally we reach back 13 billion years ago when the Big Bang occurred.