Planck 2013 results. XXVII. Doppler boosting of the CMB: eppur si muove

Our velocity relative to the rest frame of the cosmic microwave background (CMB) generates a dipole temperature anisotropy on the sky which has been well measured for more than 30 years, and has an accepted amplitude of v=c = 1:23 _ 103, or v = 369 km s1. In addition to this signal generated by Doppler boosting of the CMB monopole, our motion also modulates and aberrates the CMB temperature fluctuations (as well as every other source of radiation at cosmological distances). This is an order 103 effect applied to fluctuations which are already one part in roughly 105, so it is quite small. Nevertheless, it becomes detectable with the all-sky coverage, high angular resolution, and low noise levels of the Planck satellite. Here we report a first measurement of this velocity signature using the aberration and modulation effects on the CMB temperature anisotropies, finding a component in the known dipole direction, (l; b) = (264_; 48_), of 384 km s1 _ 78 km s1 (stat:) _ 115 km s1 (syst:). This is a significant confirmation of the expected velocity.