The ARCADE 2 instrument has measured the absolute temperature of the sky at frequencies 3, 8, 10, 30, and 90 GHz, using an open-aperture cryogenic instrument observing at balloon altitudes with no emissive windows between the beam-forming optics and
the sky. An external blackbody calibrator provides an {it in situ} reference. Systematic errors were greatly reduced by using differential radiometers and cooling all critical components to physical temperatures approximating the CMB temperature. A linear model is used to compare the output of each radiometer to a set of thermometers on the instrument. Small corrections are made for the residual emission from the flight train, balloon, atmosphere, and foreground Galactic emission. The ARCADE 2 data alone show an extragalactic rise of $50pm7$ mK at 3.3 GHz in addition to a CMB temperature of $2.730pm .004$ K. Combining the ARCADE 2 data with data from the literature shows a background power law spectrum of $T=1.26pm 0.09$ [K] $( u/ u_0)^{-2.60pm 0.04}$ from 22 MHz to 10 GHz ($ u_0=1$ GHz) in addition to a CMB temperature of $2.725pm .001$ K.
The rotating reference system, two-point correlation functions, and energy density are used as the basis for investigating thermal effects observed by a detector rotating through random classical zero-point radiation. The RS consists of Frenet -Serre
t orthogonal tetrads where the rotating detector is at rest and has a constant acceleration vector. The CFs and the energy density at the rotating reference system should be periodic with rotation period because CF and energy density measurements is one of the tools the detector can use to justify the periodicity of its motion. The CFs have been calculated for both electromagnetic and massless scalar fields in two cases, with and without taking this periodicity into consideration. It turned out that only periodic CFs have some thermal features and particularly the Plancks factor with the temperature T= h w /k . Regarding to the energy density of both electromagnetic and massless scalar field it is shown that the detector rotating in the zero-point radiation observes not only this original zero-point radiation but, above that, also the radiation which would have been observed by an inertial detector in the thermal bath with the Planks spectrum at the temperature T. This effect is masked by factor 2/3(4 gamma^2-1) for the electromagnetic field and 2/9 (4 gamma ^2-1) for the massless scalar field, where the Lorentz factor gamma=(1 - v^2 / c^2)^(1/2). Appearance of these masking factors is connected with the fact that rotation is defined by two parameters, angular velocity w and the radius of rotation, in contrast with a uniformly accelerated linear motion which is defined by only one parameter, acceleration a. Our calculations involve classical point of view only and to the best of our knowledge these results have not been reported in quantum theory yet.
