In the study of orbital dynamics the mean anomaly is a measure of time, specific to the orbiting body p, which is a multiple of 2π radians at and only at periapsis. It is the fraction of the orbital period that has elapsed since the last passage at periapsis z, expressed as an angle. In the diagram below, it is M (the angle z-c-y).

The point y is defined such that the circular sector area z-c-y is equal to the elliptic sector area z-s-p, scaled up by the ratio of the major to minor axes of the ellipse.

Calculation

In astrodynamicsmean anomaly can be calculated as follows:

The eccentricanomaly is observed from the centre of the ellipse, using a projection of the planet's position onto the circumscribing circle; and

The meananomaly is the fraction of an orbital period that has elapsed, expressed as an angle.

In spacecraft operations, an anomaly is an event that results in an unexpected and unwanted event that may cause a negative impact to the state of health of the spacecraft.

Mean R anomaly is the anomaly which the body would have if it moved from the pericentre around F with a uniform angular motion such that its revolution would be completed in its actual time (see Orbit).

Eccentricanomaly is defined thus: - Draw the circumscribing circle of the elliptic orbit around the centre C of the orbit.

In the ancient astronomy the anomaly was taken as the angular distance of the planet from the point of the farthest recession from the earth.

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