Skip to main content

Paleoclimatology (thesaurus)

Search from vocabulary

align
annotate
download

Concept information

natural phenomenon > astronomical phenomenon > eccentricity cycle

Preferred term

eccentricity cycle  

Definition

  • The eccentricity cycle: this refers to the variation in the shape of the Earth's orbit, which oscillates between a more circular and a more elliptical shape. The main cycle has a period of around 400,000 years, with secondary cycles of the order of 100,000 years. In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values between 0 and 1 form an elliptic orbit, 1 is a parabolic escape orbit (or capture orbit), and greater than 1 is a hyperbola. The term derives its name from the parameters of conic sections, as every Kepler orbit is a conic section. It is normally used for the isolated two-body problem, but extensions exist for objects following a rosette orbit through the Galaxy. Orbital mechanics require that the duration of the seasons be proportional to the area of Earth's orbit swept between the solstices and equinoxes, so when the orbital eccentricity is extreme, the seasons that occur on the far side of the orbit (aphelion) can be substantially longer in duration. Northern hemisphere autumn and winter occur at closest approach (perihelion), when Earth is moving at its maximum velocity—while the opposite occurs in the southern hemisphere. As a result, in the northern hemisphere, autumn and winter are slightly shorter than spring and summer—but in global terms this is balanced with them being longer below the equator. In 2006, the northern hemisphere summer was 4.66 days longer than winter, and spring was 2.9 days longer than autumn due to orbital eccentricity. Apsidal precession also slowly changes the place in Earth's orbit where the solstices and equinoxes occur. This is a slow change in the orbit of Earth, not the axis of rotation, which is referred to as axial precession. The climatic effects of this change are part of the Milankovitch cycles. (Adapted from: https://en.wikipedia.org/wiki/Orbital_eccentricity and Adapted and translated from: https://fr.wikipedia.org/wiki/Cycles_de_Milankovitch)

Broader concept

In other languages

URI

http://data.loterre.fr/ark:/67375/QX8-9T616NP8-B

Download this concept:

RDF/XML TURTLE JSON-LD