
A space telescope that observed hundreds of thousands of stars to detect planets by their transits.The Kepler telescope was a space observatory launched by NASA in 2009 to discover exoplanets, particularly Earth-sized planets in the habitable zone of their stars. It monitored over 150,000 stars in a fixed field of view, looking for periodic dips in brightness caused by a planet transiting in front of its host star. Kepler's mission fundamentally changed our understanding of planetary systems, revealing that planets are common and that many are unlike anything in our solar system.
The Kepler mission was proposed in the 1980s by William Borucki and launched on March 7, 2009. It operated until 2018, having discovered over 2,600 confirmed exoplanets.
Kepler used the transit method: a sensitive photometer measured the brightness of thousands of stars every few minutes. A planet passing in front of its star blocks a tiny fraction of light, producing a periodic dimming. By analyzing the depth, duration, and timing of these dips, astronomers can infer the planet's size, orbital period, and sometimes even its atmosphere.
Kepler's data has been used to statistically estimate the frequency of Earth-like planets in the galaxy, guiding future missions like TESS and the James Webb Space Telescope in targeting promising systems.
Kepler's field of view covered only about 0.25% of the sky, yet it found thousands of planets, implying that there are likely billions of planets in our galaxy alone.




















