What is meant by Apogee and perigee,Eccentricity? How do we Calculate them?
Apogee, perigee and eccentricity are terms which describe aspects of an elliptic orbit.
Planets, moon and satellites follow elliptic orbits. There are a number of parameters which can be used to describe an orbit. At least two parameters are required.
The semi-major axis
Apogee means the furthest distance the Moon or a satellite gets from Earth in its orbit. The related term aphelion is the furthest distance a planet or other body gets from the Sun. The generic term is apapsis which describes the furthest distance an orbit gets from anything. Apogee
Perigee means the closest distance the Moon or a satellite gets to Earth in its orbit. The related term perihelion is the closest distance a planet or other body gets to the Sun. The generic term is periapsis which describes the closest distance an orbit gets to anything. Perigee
Given any two of apogee, perigee, eccentricity and semi-major axis, it is easy to calculate the other two and completely define the ellipse.