In general, a deviation from the norm.
An angle that gives the position of an object in an elliptical orbit
at any given time with respect to its primary. The true anomaly
is the angle between the periapsis
of an orbit and the object's current orbital position, measured from
the body being orbited and in the direction of orbital motion. The
mean anomaly is what the true anomaly would be if the object orbited
in a perfect circle at constant speed.

Of a planetary orbit,
the angle measured from the perihelion position, to the center of the circumscribing
auxiliary circle, to the projected position of the planet on the circle.
→ anomaly; → mean anomaly;
→ true anomaly.

The angle between the periapsis of an orbit and the position of a
hypothetical body that orbits in the same period as the real one but at a constant
mean angular velocity.

A region of the Earth where the inner → Van Allen belt
comes closest to the Earth's surface. It is due to the fact that the
→ geomagnetic field is offset from the center of the Earth.
The region is centered near 25 degrees South 50 degrees West, close to the Atlantic
coast of Brazil. The excess of trapped energetic particles in that region presents
a problem for satellites in orbit around the Earth.

One of the standard → orbital elements, which is
the angle measured at the → focus
nearest the → periapsis
of an elliptical orbit, between the periapsis and the
→ radius vector from the focus to the orbiting body.