📐 Space Glossary

Orbital Elements

The six classical Keplerian elements that fully describe a satellite's orbit — defining its size, shape, orientation, and the position of the satellite within it. 11 terms, each explained in plain language with key data and links to live trackers.

Apogee & Perigee Highest & lowest points of an orbit 250 km35,786 km ω Argument of Perigee Angle from ascending node to perigee — orbit orientation 0°–360°63.4° (no precession) e Eccentricity How elliptical an orbit is — 0 to 1 0.00010.0002 t₀ Epoch Reference time for orbital data validity YYDDD.DDDDDDDDUTC i Inclination Orbital tilt angle — 0° to 180° 0°–180°90° M Mean Anomaly Where the satellite is in its orbit at epoch 0°–360°0° MM Mean Motion Orbits per day — encodes orbital size 15.5 rev/day1.0 rev/day OP Orbital Period Time per orbit — determined by altitude 92 min12 hours Ω RAAN Where the orbit crosses the equator going north Ω (Omega)0–360° a Semi-Major Axis Half the longest diameter of an orbit — defines size ~6,790 km26,560 km ν True Anomaly Actual geometric angle of satellite from perigee 0°–360°0°

More glossary categories

All terms 🌐 Orbit Types 📡 Tracking & Space Surveillance 🚀 Manoeuvres & Propulsion 🛡️ Debris & Space Safety 🛰️ Spacecraft Systems 🏗️ Launch & Ascent ☀️ Space Environment ⚖️ Policy & Regulation 📍 Navigation & Timing 🔭 Earth Observation 📡 Amateur Radio & Satellites 🔭 Deep Space & Astrophysics 👨‍🚀 Human Spaceflight 🌐 Satellite Internet & Mega-Constellations 🪐 Planetary Science & Exploration