Galaxy

A galaxy is a massive, gravitationally bound collection of stars, gas, dust, and invisible dark matter that forms some of the universe's most spectacular structures. Think of galaxies as cosmic cities, each containing anywhere from a few million stars in small dwarf galaxies to over a trillion stars in massive elliptical giants.</p><p>Our home galaxy, the Milky Way, is a spiral galaxy containing approximately 100-400 billion stars and measuring about 100,000 light-years across. On clear, dark nights, you can actually see part of our galaxy as a faint, milky band stretching across the sky—which is how it got its name. The nearest major galaxy to us is Andromeda, located 2.5 million light-years away and containing roughly one trillion stars.</p><p>Galaxies come in three main shapes: spirals with graceful arms (like the Milky Way), smooth ellipticals, and irregular galaxies with no defined structure. The term "galaxy" comes from the Greek word "galaxias," meaning milky, first used by ancient Greeks to describe the Milky Way. Until the 1920s, astronomers thought our galaxy was the entire universe! Edwin Hubble's discovery that other galaxies existed beyond our own revolutionized our understanding of the cosmos, revealing a universe containing over two trillion galaxies, each a vast island of stars in the cosmic ocean.