Orbital variations (main)
From The Encyclopedia of Earth
Orbital variations
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Solar Energy: The Major Driver of Earth's...The major driver of Earth’s climate is the amount of solar energy it receives. Three laws relate the solar energy reaching Earth to the planet’s orientation with... More »
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Solar Energy: The Major Driver of Earth's Climate Last Updated on 2010-12-18 00:00:00 The major driver of Earth’s climate is the amount of solar energy it receives. Three laws relate the solar energy reaching Earth to the planet’s orientation with the sun. The first is the cosine law, which explains many of the differences in climate between the equator and the poles. Sunbathers instinctively obey this law in orienting themselves perpendicular to the sun to maximize the interception of solar rays or more parallel to the sun to decrease interception. The more slanted (or oblique) the angle between the sunbather and the sun, the greater the area over which a given amount of solar energy is distributed and, thus, the smaller the energy per unit area. Moreover, at the oblique angle near the poles, solar energy passes a longer distance through the atmosphere and is more likely to be reflected or absorbed by gases or particles in the atmosphere before... More » 
Orbital Variations and Solar Energy Last Updated on 2010-12-16 00:00:00 Three characteristics of Earth’s orbit around the sun—obliquity, eccentricity, and precession—change periodically and influence the amount of energy that Earth receives from the sun. Earth’s daily rotation around its own axis currently has an angle of 23.4° with respect to its orbital plane around the sun. This angle is called the axial tilt or obliquity. The planet, however, wobbles like a spinning top, and the obliquity oscillates between 22.1° and 24.5 every 41,000 years. This means that the seasonal differences in the amount of solar energy reaching Earth varies with a period of 41,000 years. At the extremes, the current Tropic of Cancer (latitude 23.4°N) would receive about a 4.5% change in solar energy from minimum to maximum tilt. The elliptical shape of Earth’s orbit around the sun is characterized by its eccentricity, a... More » 
Milankovitch cycles (Orbital variations) Last Updated on 2010-07-07 16:09:56 Milankovitch cycles refer to long term variations in the orbit of the Earth which result in changes in climate over periods hundred of thousands of years and are related to ice age cycles. Once Isaac Newton described his laws of motion and of gravity, the orbit of each planet became predictable, not only under the influence the Sun, but the much weaker influences of all the other planets and the Moon as well. Milutin Milankovitch did not discover the cycles, nor was he the first to calculate their changes. He did, though, improve on the methods of calculating them and relating them to Earth’s climatic variations. Here is a brief description of the three cycles. Precession (also called Precession of the Equinoxes): the gravitational pull of the Sun and Moon on Earth’s equatorial bulge causes the poles to slowly wobble. Over 25,800 years, the polar axis... More » 
