Binary star systems consist of two stars gravitationally bound together, orbiting around their shared center of mass called the barycenter. Far from being cosmic oddities, binary systems are extraordinarily common—astronomers estimate that over half of all stars exist in binary or multiple star systems, making our solitary Sun somewhat unusual.</p><p>These stellar partnerships come in fascinating varieties. Visual binaries like Albireo in Cygnus can be separated through telescopes, revealing a beautiful golden-orange star paired with a blue companion. Eclipsing binaries such as Algol in Perseus regularly dim when one star passes in front of the other, creating predictable "winking" every 2.87 days that ancient astronomers called the "Demon Star." Spectroscopic binaries are detected through the Doppler shift of their light as they orbit, even when too close to resolve visually.</p><p>Binary systems serve as cosmic laboratories, allowing astronomers to determine stellar masses through orbital mechanics—something impossible with single stars. The first binary star, Mizar in the Big Dipper, was discovered in 1650, revolutionizing our understanding that stars aren't always solitary. These systems can evolve dramatically: when one star becomes a white dwarf and strips material from its companion, it can trigger spectacular nova explosions, making binaries crucial players in stellar evolution and the chemical enrichment of galaxies.