A star is a massive, glowing ball of hot gas (called plasma) held together by its own powerful gravity. Deep within a star's core, temperatures reach over 10 million degrees Celsius, hot enough to fuse hydrogen atoms into helium through nuclear fusion—the same process that powers hydrogen bombs but sustained over billions of years. This fusion releases tremendous energy that travels outward, making stars shine and providing the light and heat we see.</p><p>Our Sun is a typical medium-sized star, containing 99.8% of our solar system's mass and burning through 600 million tons of hydrogen every second. The closest star beyond our Sun is Proxima Centauri, located 4.2 light-years away—so distant that its light takes over four years to reach Earth. Stars come in various sizes: red dwarf stars can be as small as 8% of the Sun's mass, while massive blue giants can exceed 100 times the Sun's mass.</p><p>Ancient civilizations used stars for navigation and timekeeping, creating constellations that we still recognize today. Modern astronomy reveals that stars are cosmic factories, forging heavy elements like carbon, oxygen, and iron in their cores—elements essential for planets and life itself. When massive stars die in spectacular supernova explosions, they scatter these materials across space, seeding future generations of stars and planetary systems.
Examples
**Example:** Our Sun is a medium-sized yellow dwarf star with a surface temperature of about 5,500°C. The red supergiant Betelgeuse is so large that if placed at the center of our Solar System, it would extend past the orbit of Mars.