- Apogee: A farthest point from the Earth’s surface in an orbit is known as Apogee.
- Perigee: A nearest point from the Earth’s surface in an orbit is known as Perigee.
- Ascending node: The point at which satellite intersects the equatorial plane while going from south to north.
- Descending node: The point at which satellite intersects the equatorial plane going from north to south.
- Right Ascension of the ascending node (Ω): It is the angle measured eastward in the equatorial plane from the line of aries to the ascending node. Thus, Ω is the longitude of the ascending node.
- Argument of Perigee (ω): The angle from the ascending node to the Perigee measured in the orbital plane at the earth’s center in the direction of motion.
- Eccentric Anomaly (E): It is the central angle measured from X-axis to the vertical projection of a satellite over the circle of radius a. It is given as:
$cosE=\frac{e+cos v}{1+ecosv}$
$where, e – eccentricity$
$v - True anomaly$
- Mean Anomaly (M): It may be considered as True Anomaly if the satellite would have proceeded along a circular orbit of the same period T as that of the elliptical orbit. Mean anomaly gives average value of the angular position of the satellite with reference to Perigee.
$M=E-esinE$
$where, E – Eccentric anomaly$
$e - eccentricity$