This glossary assists you in understanding the basic terms that are frequently used when referring to satellite orbits. 

ALTITUDE 
The shortest distance of the satellite from the Earth's surface at a given time. This can also be called the Height. This can also refer to an observer's distance above sea level (as in aircraft altitude).
It is symbolized by the
letter "A". 
APOGEE  
ARGUMENT OF LATITUDE 
The angle formed from the satellite orbit's ascending node to the satellite orbit's perigee point in the direction of the satellite's travel. It is basically the addition of the satellite orbit's Argument of Perigee (w) and the satellite's True Anomaly (n). It is symbolized by the Greek letter "m".
m
=
w
+
n 
ARGUMENT OF PERIGEE  CLICK HERE 
ASCENDING NODE  CLICK HERE 
CARTESIAN COORDINATES 
A coordinate system based solely on linear components (no angles). A threedimensional Cartesian coordinate system has three components; normally symbolized by the letters x, y and z. 
DESCENDING NODE  CLICK HERE 
ECCENTRIC ANOMALY  CLICK HERE 
ECCENTRICITY  CLICK HERE 
ELLIPSE  The oval shape that is assumed by all satellite orbits. 
EPOCH  CLICK HERE 
EQUATORIAL COORDINATES 
A coordinate system with one axis
parallel to the
equatorial plane
of the Earth. Normally, its components are Right Ascension (R.A.
or a)
and Declination (Dec. or d). 
EQUATORIAL PLANE 
The plane formed by the Earth's equator projected outward into infinity. 
FOCI 
The two points on the inside of an orbit's ellipse such that all rays emanating from one of the foci will reflect off the inner walls and pass through the other focus. 
FOCUS DISTANCE  CLICK HERE 
GEOCENTRIC 
With respect to the true (gravitational) center of the Earth. 
GEODETIC 
With respect to the point created by the intersection of the Nadir (antizenith) line and the Earth's equatorial plane. This is mainly used to correct for the spheroid (nonspherical) Earth. 
HEIGHT 
The shortest distance of the satellite from the Earth's surface at a given time. This can also be called the Altitude.
It is symbolized by the letter "h". 
KEPLER'S EQUATION  CLICK HERE 
INCLINATION  CLICK HERE 
MEAN ANOMALY  CLICK HERE 
MEAN MOTION  CLICK HERE 
ORBIT 
The path that a satellite assumes about the Earth. 
ORBIT PLANE  The plane that is formed by the satellite's orbit motion as it sweeps out one complete orbit. 
ORBIT PROPAGATION  Using a satellite's orbit elements to predict where the same satellite will be within its orbit at a future (or past) time. 
PERIGEE  CLICK HERE 
PERIOD  CLICK HERE 
POLAR COORDINATES 
A coordinate system based on one
linear term and two angular terms. For instance, a satellite's location might be
indicated by using its equatorial angular coordinates
(a,
d)
and its linear
range
(r). 
PRECESSION 
The apparent periodic motion of a
satellite orbit's
ascending node
(and other elements) due to gravitational and other external forces.
A satellite's orbit will precess
according to its orbit
inclination
and orbit
period. 
PROGRADE  The perceived counterclockwise motion of a satellite when its motion in its orbit is viewed from the north of the Earth's equatorial plane. A prograde orbit is quantitatively expressed by an orbit inclination of less than 90 degrees. 
RADIANS 
A method of measuring angles based
on the units of pi (p).
p/2
radians is equivalent to 90^{o},
p
radians is equivalent to 180^{o},
2p
radians is equivalent to 360^{o}, etc.
To convert from degrees to
radians, multiply by p/180^{o}. 
RANGE 
The direct distance of the satellite from
a point on the Earth.
It is symbolized by the letter "r". 
RETROGRADE 
The perceived clockwise motion of a satellite when its motion in its orbit is viewed from the north of the Earth's equatorial plane. A retrograde orbit is quantitatively expressed by an orbit inclination of greater than 90 degrees. 
RIGHT ASCENSION OF THE ASCENDING NODE  CLICK HERE 
SEMIMAJOR AXIS  CLICK HERE 
SEMIMINOR AXIS  
TRUE ANOMALY  CLICK HERE 
SITE MAP  
Glossary of Terms Was Last Modified On May 23, 2010 