Showing papers by "Fraunhofer Society published in 1969"
TL;DR: In this article, a preliminary analysis of recent measurements of the brightness ratio spot-photosphere of various authors leads to the result, that the limb-darkening of the umbra is considerably less than that of the photosphere.
Abstract: A preliminary analysis of recent measurements of the brightness ratio spot-photosphere of various authors leads to the result, that the limb-darkening of the umbra is considerably less than that of the photosphere. The small value of the center-to-limb variation implies a very small temperature gradient, which is, for optical depths τ>0.2, about one order of magnitude smaller than previously thought (Figure 3). This result would seem to rule out radiative equilibrium in the deeper layers (τ\S>0.2) of sunspot umbrae.
15 citations