The article by D. J. Fixsen reviews the measurements of the cosmic microwave background (CMB) temperature using the Far Infrared Absolute Spectrophotometer (FIRAS) and the Wilkinson Microwave Anisotropy Probe (WMAP) data. The FIRAS data, independently recalibrated using WMAP data, yields a CMB temperature of 2.7260±0.0013 K. The WMAP data, which measures the difference in intensity between different points on the sky, is used to calibrate the velocity of the spacecraft relative to the surface of last scattering of the CMB. This velocity is then used to form a differential spectrum of the CMB, which is fit with a single parameter—CMB temperature. The WMAP velocity maps are corrected to the baricenter of the solar system and the spacecraft velocity is used to calibrate the maps. The FIRAS data is fit to a set of ten templates, including the WMAP velocity map, to determine the CMB temperature. The uncertainty in the FIRAS measurements is dominated by noise, leading to an uncertainty estimate of 1.09 mK. The uncertainty from the WMAP measurements is also considered, and the final uncertainty in the CMB temperature is estimated to be 1.3 mK. Combining all recent precision estimates results in an improved absolute temperature estimation of 2.72548±0.00057 K. The article concludes that all recent estimates of the CMB temperature agree within 2.5 times their uncertainties, and the final estimate is significantly elevated with a modestly increased $\chi^{2}$.The article by D. J. Fixsen reviews the measurements of the cosmic microwave background (CMB) temperature using the Far Infrared Absolute Spectrophotometer (FIRAS) and the Wilkinson Microwave Anisotropy Probe (WMAP) data. The FIRAS data, independently recalibrated using WMAP data, yields a CMB temperature of 2.7260±0.0013 K. The WMAP data, which measures the difference in intensity between different points on the sky, is used to calibrate the velocity of the spacecraft relative to the surface of last scattering of the CMB. This velocity is then used to form a differential spectrum of the CMB, which is fit with a single parameter—CMB temperature. The WMAP velocity maps are corrected to the baricenter of the solar system and the spacecraft velocity is used to calibrate the maps. The FIRAS data is fit to a set of ten templates, including the WMAP velocity map, to determine the CMB temperature. The uncertainty in the FIRAS measurements is dominated by noise, leading to an uncertainty estimate of 1.09 mK. The uncertainty from the WMAP measurements is also considered, and the final uncertainty in the CMB temperature is estimated to be 1.3 mK. Combining all recent precision estimates results in an improved absolute temperature estimation of 2.72548±0.00057 K. The article concludes that all recent estimates of the CMB temperature agree within 2.5 times their uncertainties, and the final estimate is significantly elevated with a modestly increased $\chi^{2}$.