Geocentric Orbit - List of Terms and Concepts

List of Terms and Concepts

Altitude

as used here, the height of an object above the average surface of the Earth's oceans.

Analemma

a term in astronomy used to describe the plot of the positions of the Sun on the celestial sphere throughout one year. Closely resembles a figure-eight.

Apogee

is the farthest point that a satellite or celestial body can go from Earth, at which the orbital velocity will be at its minimum.

Eccentricity

a measure of how much an orbit deviates from a perfect circle. Eccentricity is strictly defined for all circular and elliptical orbits, and parabolic and hyperbolic trajectories.

Equatorial plane

as used here, an imaginary plane extending from the equator on the Earth to the celestial sphere.

Escape velocity

as used here, the minimum velocity an object without propulsion needs to have to move away indefinitely from the Earth. An object at this velocity will enter a parabolic trajectory; above this velocity it will enter a hyperbolic trajectory.

Impulse

the integral of a force over the time during which it acts. Measured in (N·sec or lb * sec).

Inclination

the angle between a reference plane and another plane or axis. In the sense discussed here the reference plane is the Earth's equatorial plane.

Orbital characteristics

the six parameters of the Keplerian elements needed to specify that orbit uniquely.

Orbital period

as defined here, time it takes a satellite to make one full orbit about the Earth.

Perigee

is the nearest approach point of a satellite or celestial body from Earth, at which the orbital velocity will be at its maximum.

Sidereal day

the time it takes for a celestial object to rotate 360°. For the Earth this is: 23 hours, 56 minutes, 4.091 seconds.

Solar time

as used here, the local time as measured by a sundial.

Velocity

an object's speed in a particular direction. Since velocity is defined as a vector, both speed and direction are required to define it.