Consider the case of Figure 1 in which an observer in space observes the earth at radio frequencies. In particular, consider the radio brightness distribution in one dimension; i.e. let the observer look at the earth such that he looks in the equatorial plane of the centered dipole model for the geomagnetic field. The question to be considered is how does the radio brightness b vary with the direction and frequency of observation. An estimate of b(R, ƒ) is made below assuming that the electrons in the Van Allen belts radiate in the synchrotron mode.