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Stars are primarily composed of hydrogen and helium, which together account for about 98% of their mass. Through the process of nuclear fusion occurring in their cores, these elements undergo reactions that release vast amounts of energy, producing the light and heat we observe from Earth. As stars evolve, they can create heavier elements such as carbon, oxygen, and iron through fusion processes, contributing to the cosmic abundance of these materials. Ultimately, the composition of a star not only defines its lifecycle but also influences the formation of planets and the potential for life in the universe.