What Is Sunlight?
What Is Sunlight? by Glen Hobby 24 December 2025 Introduction Sunlight is often described simply as “light from the Sun,” but this description barely scratches the surface. Scientifically, sunlight is a continuous stream of electromagnetic radiation produced by nuclear reactions in the Sun’s core and transmitted across space to Earth. Understanding sunlight means understanding astrophysics , atmospheric science , biology , and climate — all of which directly influence weather and forecasting. This article explores sunlight in greater depth, from its origin inside the Sun to its role in shaping Earth’s environment. The Physical Origin of Sunlight The Sun is a main-sequence star composed primarily of hydrogen and helium . At its core, temperatures exceed 15 million degrees Celsius, and pressures are high enough to force hydrogen nuclei to fuse together. This nuclear fusion process converts hydrogen into helium through a series of reactions known as the proton–proton chain . In each...