SOLAR SYSTEM

Detailed explanation-1: -The eccentricity of an orbit is a single number, between 0 and 1, which describes how stretched out the orbit is. Zero means the orbit is perfectly circular. An eccentricity close to 1 means the orbit is extremely elongated; only comets coming from the outer reaches of the solar system get close to this value.

Detailed explanation-2: -As eccentricity increases, for example, the seasons at aphelion grow longer and colder, while those at perihelion grow shorter and warmer. The range in seasonality also becomes more extreme during periods of larger eccentricity.

Detailed explanation-3: -Radial orbits have zero angular momentum and hence eccentricity equal to one.

Detailed explanation-4: -In a stricter sense, it is a Kepler orbit with the eccentricity greater than 0 and less than 1 (thus excluding the circular orbit). In a wider sense, it is a Kepler orbit with negative energy. This includes the radial elliptic orbit, with eccentricity equal to 1.