The Sun is the most prominent feature in the Solar System. One hundred and nine Earths could fit across the disk of the Sun, and over a million Earths could fit inside. The Sun has been active for about 4.6 billion years, and has enough energy to to last for another 5 billion. The Sun produces energy inside of its core where hydrogen is turned into helium through nuclear reactions. As the hydrogen is used up, the Sun swells and will eventually become a red giant star. After a billion years or so as a red giant, it will collapse into a white dwarf star- the end product of a star like ours.
The core of the Sun is a sizzling 15 million degrees Celsius. The surface, called the photosphere, has a typical temperature if 6,000 degrees Celsius. The Sun has an atmosphere, called the chromosphere. The chromosphere can be as hot as the Sun's core. Sunspots, the dark regions of the Sun, are areas that are cooler than the rest of the surface; generally around 4,000 degrees Celsius. Sunspots are actually very bright, but appear dark in contrast to its brillant surroundings.
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