A star is a massive, luminous ball of plasma, which are scattered throughout the universe. Stars group together to form galaxies, and they dominate the visible universe. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth, including daylight. Other stars are visible in the night sky, when they are not outshone by the Sun. A star shines because nuclear fusion in its core releases energy which traverses the star's interior and then radiates into outer space. Almost all elements heavier than hydrogen and helium were created inside the cores of stars.
Stars burn for million years, giving off both light and heat. The coolest stars are red and dim, while the hottest stars give off blue-white light. The temperatures on the surface range from 3,500 C for cooler stars to over 40,000 C for the hottest stars.
A new star is born when gas and dust are drawn together by gravity, forming a huge clump. It heats up until nuclear fusion begins, and the new star appears
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