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 ====== 4. Planetary Age ======
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+===== - Telescope =====
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+The Kepler Space Telescope, the definitive instrument for the Planetary Age in the AST 100 curriculum, revolutionized our understanding of the cosmos by transitioning exoplanet study from theory to statistical reality. Launched in 2009, Kepler utilized a high-resolution photometer to monitor over 150,000 stars simultaneously in a fixed field of view within the Cygnus and Lyra constellations. By detecting the minute, periodic dimming of starlight caused by a planet crossing in front of its host star—a technique known as the transit method—Kepler proved that planets are ubiquitous throughout our galaxy.
+Technologically, Kepler’s mission was defined by its incredible precision, capable of detecting brightness changes as small as twenty parts per million. This sensitivity allowed it to identify "Earth-size" planets orbiting within the habitable zones of Sun-like stars, where liquid water could potentially exist on the surface. The data history of the mission includes the discovery of over 2,700 confirmed exoplanets and thousands of additional candidates, revealing a startling diversity of worlds, from "Super-Earths" to "Hot Jupiters," that challenged existing models of solar system formation and paved the way for future atmospheric studies.
+In the broader context of cosmic history, Kepler’s legacy provides the essential bridge between the Stellar Age and the Chemical Age. By identifying the frequency of planetary systems, it shifted the scientific focus from how stars form to how frequently they produce environments capable of hosting complex chemistry. Although the primary mission ended in 2018, its vast archive of data continues to be mined by researchers and "citizens of the universe" alike. These discoveries ensure that the study of the Planetary Age remains a cornerstone of our efforts to map our place among the stars.