Short answers, pulled from the story.
Walter Munk published a paper in 1953 describing how the shape of an orbit determines its fate. Orbital eccentricity serves as a dimensionless measure for astrodynamics that defines how much an astronomical object deviates from circular motion around another body.
The term eccentricity first appeared in English during the year 1551 with a definition describing circles where earth or sun deviate from their centers. The word derives from Medieval Latin eccentricus which itself comes from Greek ekkentros meaning out of center.
Mercury holds the greatest orbital eccentricity among all planets at 0.2056 according to current measurements. Venus possesses the lowest eccentricity of any planet at just 0.0068 making its orbit nearly perfect.
In 2006 northern hemisphere summer lasted 4.66 days longer than winter due to orbital mechanics. Northern autumn and winter occur at closest approach when Earth moves fastest creating shorter seasons while southern hemisphere experiences opposite timing.
HD 20782 b holds the most eccentric known exoplanetary orbit measuring 0.97 plus or minus 0.01. Most discovered exoplanets display higher eccentricity than any Solar System planet currently observed.