The Aperture Size of Telescopes

Chapter 16 examines the historical and ongoing growth of telescope aperture size, which determines light-collecting capability and thus observational power. Since the early 1600s, when Hans Lipperhey filed the first telescope patent and Galileo used a 15-mm lens for astronomical observations, aperture areas have increased exponentially, doubling roughly every 23–24 years. Early telescopes were refractors, but Newton introduced the reflector design, which became dominant for large instruments. By the late 20th century, telescopes like the Keck pair reached 10-m mirrors, creating a plateau until recent projects such as the Giant Magellan Telescope (25.4 m) and the European Extremely Large Telescope (30 m) pushed sizes dramatically higher. Space-based telescopes like Hubble and James Webb remain smaller but avoid atmospheric distortion, while ground-based observatories use adaptive optics to compensate. This long-term trend reflects centuries of innovation, enabling deeper exploration of the cosmos and continuing toward even larger designs.