Abstract

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 ∆T = 3.365±0.027 mK toward direction (l^II, b^II) = (264°.4±0°.3, 48°.4±0°.5). The implied velocity of the Local Group with respect to the CMB rest frame is υ_LG = 627±22 km s^-1 toward (l^II, b^II) = (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 T₀ at 31.5, 53, and 90 GHz, T₀ = 2.75±0.05 K.