Star around which the solar system revolves. About 5 billion years old, it is the dominant body of the system, with more than 99% of its mass. It converts 5 million tons of matter into energy every second by nuclear fusion reactions in its core, producing neutrinos (see solar neutrino problem) and solar radiation. The small amount of this energy that penetrates earth's atmosphere provides the light and heat that support life. Solar radiation can also supply electrical power (see solar cell).