The Sun is our star and is the source of life on Earth. It keeps Earth warm enough to sustain life and provides sunlight to plants for making food and oxygen. The sun has three layers, known as the core, radiative layer, and the convective layer. In the innermost region, the core, nuclear fusion reactions take place and power the sun. The radiative and convective layers are so named because the dominant mode of heat transfer is radiation and convection in these layers, respectively. The outer parts of the sun are the photosphere, chromosphere and the corona. The photosphere is the only portion of the sun that we can see and is the lowest layer of the sun's atmosphere. The chromosphere separates the photosphere and the corona. The corona is the hottest layer of the sun.
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