Milankovitch cycles alter solar radiation distribution causing climate variations over thousands of years. Eccentricity varies from 0 to 0.0679 over 100,000-405,000 year cycles. Obliquity cycles every 41,000 years between 22.1° and 24.5°. Axial precession cycles every 25,700 years combined with apsidal precession into 21,000-year cycle. Insolation at 65° north drives glaciation due to land's rapid temperature response. Higher eccentricity amplifies seasonal solar radiation differences up to 30%. Greater tilt intensifies seasons and boosts high-latitude summer insolation. Current decreasing tilt promotes cooling and potential glacial onset. Perihelion now in northern winter shortens northern winter by 4.66 days. Ice cores confirm northern insolation forces Antarctic climate cycles. Hays-Imbrie-Shackleton validated 100,000-year eccentricity matching Quaternary ice ages. Mid-Pleistocene Transition 1 million years ago switched cycles from 41,000 to 100,000 years. Orbital forcing evident in 215 million-year rock cores. No new glacial period for next 50,000 years due to low eccentricity. Mars shows similar orbital climate cycles with 120,000-year obliquity.