Sun 101 | National Geographic

While billions of stars are scattered throughout the universe, the one at the center of our solar system plays a special role for us here on Earth. Our Sun formed about 4.5 billion years ago in the Milky Way galaxy's Orion's fur. It was born when a cloud of dust and gas, known as a solar nebula, collapsed. In the middle of this formation, matter condensed into a burning ball of gas that became our Sun.

The Sun's fiery nature, along with a tremendous gravitational pull and an extensive magnetic field, helped it to become the heart of our solar system. The Sun can be divided into six layers or regions: the corona, the chromosphere, the photosphere, the convective and radiative zones, and the core. In terms of atom count, the Sun is about 91% hydrogen, the Sun's fuel, 8.9% helium, and 0.1% heavier elements such as carbon and nitrogen.

Due to the Sun's extreme temperatures, these elements stay in a gas-like phase called plasma. In the core, temperatures reach at least 27 million degrees Fahrenheit, combined with the Sun's powerful gravity, fusing together hydrogen molecules to create helium. Called thermonuclear fusion, this releases an enormous amount of energy in the form of radiation, electricity, solar wind, and, as we experience on Earth, life-giving heat and light. Such volatility is contained thanks to the Sun's tremendous gravity.

It's strong enough to hold the solar system intact and is primarily due to the Sun's size and mass. Our Sun is the largest and most massive object in the solar system; it's more than 100 Earths wide and could theoretically fit all eight planets inside nearly 600 times. It also contains approximately 99.8% of all the mass in the solar system. Because of this mass, the Sun has a great pull on the fabric of space, creating a gravitational force that causes nearby planetary bodies to be drawn toward it.

This gravitational pull allows the Sun to hold together a system of eight planets, potentially dozens of dwarf planets, at least 170 moons, and countless comets and asteroids. Without the Sun's gravity, these celestial bodies would drift off into deep space. Another critical property of the Sun is its magnetic field, which encapsulates the entire solar system. Called the heliosphere, this force field protects the planets from harmful cosmic radiation. It's caused by the Sun's plasma pushing electrically charged particles toward the star's poles.

This process turns the Sun into a giant magnet. Although the Sun's magnetic field is invisible to the naked eye, its effects are noticeable. On the Sun's surface are dark areas called sunspots, which mark strong pockets of magnetism. On Earth and on some of the other planets, the Sun's magnetic field interacts with their atmospheres, resulting in beautiful auroras.

Despite its size and strength, the Sun will not last forever. In about 6.5 billion years, it will run out of its hydrogen fuel, expand to envelop Mercury, Venus, and even Earth, and then collapse into a small star known as a white dwarf. In the meantime, the Sun will continue to play a critical role in the system that bears its name. The Sun's protected magnetic field, tremendous gravitational pull, and ability to create vast amounts of energy will protect, contain, and give life to our solar system.