Perigee

Perigee is the point in an orbit around Earth where an object comes closest to our planet. This term comes from the Greek words "peri" (meaning near) and "gee" (meaning Earth), literally translating to "near Earth."</p><p>The concept is crucial for understanding orbital mechanics. The Moon's perigee occurs approximately every 27.3 days when it reaches its nearest approach to Earth at about 356,500 kilometers away. During perigee, the Moon appears roughly 14% larger and 30% brighter than at its farthest point (apogee), creating what many call a "supermoon."</p><p>For artificial satellites, perigee altitude determines orbital lifetime and mission capabilities. The International Space Station maintains a perigee of around 400-420 kilometers to balance atmospheric drag with operational needs. Lower perigee altitudes mean satellites experience more atmospheric resistance and decay faster, while higher altitudes extend mission duration.</p><p>The term was first used by astronomer Giovanni Cassini in the 17th century as scientists began precisely calculating lunar motion. Understanding perigee helps predict tidal variations, plan satellite missions, and time astronomical observations. Weather satellites, GPS systems, and communication networks all rely on carefully calculated perigee points for optimal performance. Ocean tides are particularly extreme during perigee, especially when combined with new or full moons, creating "perigean spring tides" that can be 20% higher than average.