Definition of orbital elements

Orbital elements are a set of parameters necessary to uniquely identify the specific orbit of a celestial body, such as a satellite or a planet. These elements describe the shape and orientation of the orbit and the position of the orbiting body along the path. The key classical orbital elements include:

• 1. Semi-major axis (a): It represents half of the longest diameter of the elliptical orbit and is a key factor in determining the size of the orbit.
• 2. Eccentricity (e): This parameter indicates the deviation of the orbit from a perfect circle. An eccentricity of 0 describes a circular orbit, while values approaching 1 represent highly elongated orbits.
• 3. Inclination (i): This angle measures the tilt of the orbit's plane with respect to the reference plane, usually the equatorial plane of the primary body.
• 4. Longitude of the ascending node (Ω): This is the angle from a reference direction, typically the direction of the vernal equinox, to the point where the orbit passes upwards through the reference plane.
• 5. Argument of periapsis (ω): This angle is between the ascending node and the orbit's point of closest approach to the central body, known as the periapsis.
• 6. True anomaly (ν): This is the angle between the direction of periapsis and the current position of the body on its orbit, measured at the central body.

These elements are fundamental in astrodynamics and celestial mechanics, allowing for the prediction and analysis of the motion of objects in space.