Fluctuations in the microwave background at large angular scale

The large-angular-scale isotropy of the cosmic background radiation is a sensitive probe of many important cosmological effects. All measurements of the angular distribution of the cosmic background radiation are consistent with only a dipole (first order spherical harmonic) anisotropy of magnitude 3 mK which is interpreted as the local solar motion relative to the comoving frame of universal expansion. All other anisotropies are less than 1 mK or one part in 3000. (Auth.)