Figure 1. Primary orbital components are displayed on the left, and Cenozoic paleogeography on the right. The gravitational forces exerted by other celestial bodies affect Earth's orbit. As a result, the amount and, more importantly, the distribution of incoming solar radiation oscillate with time (123). There are three orbital perturbations with five periods: eccentricity (at 400 and 100 ky), obliquity (41 ky), and precession (23 and 19 ky). (A) Eccentricity refers to the shape of Earth's orbit around the sun, varying from near circular to elliptical. This effect on insolation is very small, however, and by itself should not account for changes in Earth's climate during the past. (B) Obliquity refers to the tilt of Earth's axis relative to the plane of the ecliptic varying between 22.1° and 24.5°. A high angle of tilt increases the seasonal contrast, most effectively at high latitudes (e.g., winters in both hemispheres will be colder and summers hotter as obliquity increases). (C) Precession refers to the wobble of the axis of rotation describing a circle in space with a period of 26 ky. Modulated by orbital eccentricity, precession determines where on the orbit around the sun (e.g., with relation to aphelion or perihelion) seasons occur, thereby increasing the seasonal contrast in one hemisphere and decreasing it in the other. The effect is largest at the equator and decreases with increasing latitude. The periods of the precessional signal modulated by eccentricity are 23 and 19 ky, the periods observed in geological records. (D) Continental geography reconstructed for five intervals of the last 70 My designed using the commercial Paleogeographic Information System).
Orbital Mechanics: 10. Applications Of Orbit Perturbations
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