DIPOLE ANISOTROPY IN THE COBE DIFFERENTIAL MICROWAVE RADIOMETERS 1ST-YEAR SKY MAPS

We present a determination of the cosmic microwave background dipole amplitude and direction from the COBE Differential Microwave Radiometers (DMR) first year of data. Data from the six DMR channels are consistent with a Doppler-shifted Planck function of dipole amplitude DELTAT = 3.365 +/- 0.027 mK toward direction (l(II), b(II)) = (264.4-degrees +/- 0.3-degrees, 48.4-degrees +/- 0.5-degrees). The implied velocity of the Local Group with respect to the CMB rest frame is v(LG) = 627 +/- 22 km s-1 toward (l(II), b(II)) = (276-degrees +/- 3-degrees, 30-degrees +/- 3-degrees). DMR has also mapped the dipole anisotropy resulting from the Earth's orbital motion about the Solar system barycenter, yielding a measurement of the monopole CMB temperature T0 at 31.5, 53, and 90 GHz, T0 = 2.75 +/- 0.05 K.