The Solar System is our cosmic neighborhood, a gravity-bound system centered around the Sun, a medium-sized star that contains approximately 99.8% of the system’s total mass. Orbiting this central star are eight major planets: the four rocky inner planets—Mercury, Venus, Earth, and Mars—and the four outer giants—Jupiter, Saturn, Uranus, and Neptune. Beyond these planets, the system includes hundreds of moons, five officially recognized dwarf planets (such as Pluto and Ceres), and millions of smaller bodies like asteroids and comets. Formed roughly 4.6 billion years ago from a collapsing cloud of interstellar gas and dust, our solar system resides in the Orion Arm of the Milky Way galaxy and remains the only known planetary system to support life.
Stars are massive, luminous spheres of plasma held together by their own gravity and primarily composed of hydrogen and helium. They are born within vast clouds of gas and dust called nebulae, where gravity causes material to collapse until the core reaches temperatures and pressures high enough to ignite nuclear fusion. This process, which converts hydrogen into helium, releases the immense energy that makes a star shine. A star’s life cycle is almost entirely determined by its initial mass: massive stars burn through their fuel quickly and may end in violent supernova explosions, while smaller stars like our Sun burn more slowly for billions of years before eventually becoming white dwarfs. Beyond providing light, stars are the universe’s chemical “factories,” forging the heavier elements—like carbon and iron—that eventually form planets and the building blocks of life.
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