Dipole Anisotropy in the COBE Differential Microwave Radiometers First-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 ΔT = 3.365±0.027 mK toward direction (l<SUP>II</SUP>, b<SUP>II</SUP>) = (264°.4±0°.3, 48°.4±0°.5). The implied velocity of the Local Group with respect to the CMB rest frame is υ<SUB>LG</SUB> = 627±22 km s<SUP>-1</SUP> toward (l<SUP>II</SUP>, b<SUP>II</SUP>) = (276°±3°, 30°±3°). 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 T<SUB>0</SUB> at 31.5, 53, and 90 GHz, T<SUB>0</SUB> = 2.75±0.05 K.