How old is the Sun?
Short answer: About 4.6 billion years old.
Long answer: Our understanding of the Sun's age is based on a variety of evidence and interlinking theories. It incorporates research from different scientific fields from quantum mechanics to astrophysics.
The theoretical framework that describes the birth and development of solar systems like ours is called the "Nebular hypothesis". It states that a solar system (AKA planetary system) is formed over millions of years from an enormous cloud of dust and gas1. Our Sun is roughly middle-aged. We expect it to stay stable for a few billion years, then some time in about 5 billion years it will become a red giant. After that, it will become a white dwarf, slowly cooling over trillions of years.
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Author: Dave Owen