Where was WMAP positioned to observe the cosmic microwave background?

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Oval map of the cosmic microwave background radiation from NASA's WMAP mission, showing a mottled pattern of blue, green, yellow, and red representing temperature variations. — Cosmic microwave background A full-sky map produced by the Wilkinson Microwave Anisotropy Probe (WMAP) showing cosmic background radiation, a very uniform glow of microwaves emitted by the infant universe more than 13 billion years ago. Color differences indicate tiny fluctuations in the intensity of the radiation, a result of tiny variations in the density of matter in the early universe. According to inflation theory, these irregularities were the “seeds” that became the galaxies. WMAP's data support the big bang and inflation models, and cosmic microwave background is at the farthest limits of the observable universe.

The Wilkinson Microwave Anisotropy Probe (WMAP) was positioned near the second Lagrangian point (L2), which is a gravitational balance point located 1.5 million km (0.9 million miles) from Earth on the side opposite the Sun.1

Rather than remaining stationary, the spacecraft followed a controlled Lissajous pattern around this point. This specific orbital placement was chosen to isolate the probe from radio interference originating from Earth and the Moon, allowing for highly sensitive observations of the cosmic microwave background without requiring a more distant, complex trajectory.1