Overview (The Solar System)
Earth-Sun relations are the dominant controls of life on Earth. The Sun is a star, and its Electromagnetic radiation warms the Earth and supplies the energy that supports life on the planet. Earth-Sun relations determine the amount, duration, and distribution of Solar radiation that is received by Earth. The Earth’s rotation on its axis produces day and night, and its Revolution around the Sun and the tilt of its rotational axis result in the seasons; these processes serve to distribute solar radiation over the Earth. Earth’s atmosphere and oceans influence the reflection, absorption, and transfer of solar energy. The result of these interacting phenomena is a “heat budget” on Earth that is hospitable to life.
The Sun radiates electromagnetic energy from every part of its spherical surface. Earth, 150 million kilometers away, intercepts only a minute portion of the Sun’s radiation, about one two-billionth. The small amount of the Sun’s energy that strikes Earth is Earth’s energizer. It sustains life on Earth and drives weather systems and oceanic circulation. Solar energy from the past has been preserved in the form of fossil fuels—coal, petroleum, and natural gas.
Perhaps the most remarkable aspect of Earth—remarkable because it is rare in our solar system—is its relatively narrow range of moderate temperatures. The adjectives “hot” and “cold” are frequently used in describing our weather. In...
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Methods of Study (The Solar System)
The seasonal variations in the Sun’s apparent daily motion across the sky were noted by many ancient cultures. Various stone structures built hundreds to thousands of years ago around the world—from Stonehenge on England’s Salisbury Plain to Caracol in Mexico’s Yucatán peninsula to the Bighorn Medicine Wheel high in Wyoming’s Bighorn Mountains to Mystery Hill in southern New Hampshire—display alignments pointing toward the rising and setting points of the Sun on the solstices and equinoxes.
More recently it has been determined that the tilt and orientation of Earth’s rotational axis and the Eccentricity of Earth’s Elliptical orbit change slowly and cyclically with time. The tilt of Earth’s rotational axis relative to a perpendicular to the Ecliptic plane (the plane of Earth’s orbit around the Sun) now is about 23.5°, but it varies between approximately 21.5 and 24.5° over a cycle of 41,000 years. A greater tilt results in more extreme summer and winter climates, while a smaller tilt means summers are not as hot and winters are not as cold.
Earth’s rotational axis also slowly wobbles like that of a giant top, tracing out in space a double cone over a period of 26,000 years. This wobble is due to the gravitational pull of the Moon and the Sun on Earth’s equatorial bulge. At the present time, we are closest to the Sun during northern winter and farthest away during northern summer, but as a...
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Context (The Solar System)
Life on Earth is profoundly dependent upon the relationships between Earth and the Sun. The temperature of Earth is set by a balance between Earth’s absorption of electromagnetic energy from the Sun and the subsequent reradiation of that energy from Earth as heat back into space. Life on the planet is dependent on this balance and the moderate temperatures that result.
Rotation influences Earth like a rotisserie, turning the planet so as to expose all sides to the Sun during the twenty-four-hour day for a more even heat. The atmosphere protects Earth from overheating by day and from overcooling at night. Earth’s “greenhouse effect” is a result of the atmosphere’s ability to trap solar radiation as heat during the day and retard its escape back into space at night, when the Sun is not above the horizon. Earth’s heat budget is a product of many factors, not all of which are fully understood. Intense research continues on possible causes and effects of changes in Earth’s heat budget. Being able to predict future changes is of prime importance so we can either prepare for them or try to avert them.
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Further Reading (The Solar System)
Ahrens, C. Donald. Meteorology Today: An Introduction to Weather, Climate, and the Environment. 8th ed. Florence, Ky.: Brooks/Cole, 2006. This introductory college-level text on meteorology presents a thorough treatment of weather phenomena and explains the seasons and the effects of solar energy on the atmosphere. Written for students with little background in science or mathematics. Includes many illustrations.
Chaisson, Eric, and Steve McMillan. Astronomy Today. 6th ed. New York: Addison-Wesley, 2008. Very well-written college-level textbook for introductory astronomy courses. Part of one chapter deals with Earth motions and the seasons; part of another, with solar activity.
Fraknoi, Andrew, David Morrison, and Sidney Wolff. Voyages to the Stars and Galaxies. Belmont, Calif.: Brooks/Cole-Thomson Learning, 2006. A well-written, thorough college textbook for introductory astronomy courses. Has sections dealing with sky motions, the seasons, and solar activity.
Freedman, Roger A., and William J. Kaufmann III. Universe. 8th ed. New York: W. H. Freeman, 2008. College-level introductory astronomy textbook, thorough and well written. Includes sections on sky motions, the seasons, and solar activity.
Gabler, Robert E., Robert J. Sager, Sheila M. Brazier, and D. L. Wise. Essentials of Physical Geography. 8th ed. Florence, Ky.: Brooks/Cole, 2006. A general...
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