The European Space Agency’s (ESA) Planck spacecraft maintains an orbit about the second Sun-Earth Lagrangian point, called L2. (The L2 point sits some 930,000 miles [1.5 million kilometers] from Earth in the direction opposite the Sun.) From there, the probe scans the microwave sky, observing nearly all radiation with wavelengths between 0.3 millimeters and 11.1mm. For reference, visible light corresponds to energy with wavelengths between 390 nanometers and 700nm — that’s some 1,000 times shorter than microwave radiation.

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