Modern solar theory, in large part, was brought to us by Sir. A.S. Eddington, a Professor at Cambridge at the beginning of the century. Based on Eddington, scientists still maintain that the sun is largely a ball of gas. Many believe that this gas is prevented from collapsing on itself as a result of radiation pressure (X-rays) generated inside the sun. The visible surface of the sun (the photosphere) is also currently thought by many to be gaseous in nature. Based on a measurement from Langley (1880's), the photosphere is currently viewed as relatively cold at ~6,000 K. The modern model of the sun must also deal with a violation of the 2nd law of thermodynamics.