The Sun is the ultimate source of energy for life on Earth. It is 1 million times bigger than Earth but Earth only receives 1 billionth of its energy output due to its distance of 93 million miles. Some of the Sun's radiation is reflected or radiated back into space while enough remains to warm Earth and power its ecosystems. Earth's rotation causes day and night while its revolution around the Sun takes 365 days to complete. Its tilted axis and round shape cause the seasons as different hemispheres receive more direct sunlight throughout the year. Latitude affects climate zones, with the hottest temperatures at the equator and coldest at the poles due to the angle of the Sun's rays.

1. The Sun The Sun is the ultimate source of energy for life on earth (Earth’s core is the source of energy for the movement of tectonic plates) The sun is 1 million times bigger than the earth, but the earth only gets 1 billionth of it energy The sun is 93 million miles away (about 8 light minutes) Of all of the radiation that reaches earth, only a small amount reaches the surface: Some is radiated back into space by clouds Some is reflected by light colored surface (snow) Enough remains to warm the earth and provide energy for nearly all of its life forms The atmosphere also prevents heat from escaping back into space too quickly (Greenhouse Effect)

2. Earth’s Rotation and Revolution Rotation – earth spins on its axis and one complete rotation equals day and night (24 hrs) Revolution – earth revolves around the sun and completes one revolution in 365 and one quarter days; leap year adds a day to the calendar every 4 years.

3. Planetary Factors that Influence the Distribution of Heat from the Sun The earth spins on its axis so half faces the sun while the other half faces away The earth is round , therefore equatorial regions receive more direct sunlight than polar regions The earth is tilted on its axis 23 and a half degrees so at different points in its orbit around the sun, part of it receives more direct sunlight than the other, this causes SEASONS Solstices mark the periods of the earth’s orbit when one end is farthest away while the other end is closest (June 21 and December 21). Equinoxes mark the periods when all areas of the earth are equidistant from the sun (March 21 and September 21).

4. Influence of Latitude The angle of the sun’s rays are most direct at the equator and least direct, more dispersed, at the poles causing more intense heating in the mid-section (TROPICS) and more intense cold at the poles (ARCTIC).

5. Lines of Latitude enable the earth to be divided into zones that are very generally defined by CLIMATE Tropical Zones – from equator north and south to latitudes 23 degrees (north – Tropic of Cancer; south – Tropic of Capricorn); most places here are hot year around. Temperate Zones – from 23 degrees N/S to 66 degrees N/S; generally cooler with a wide variety of temperature fluctuation. Polar Zones – from 66 degrees N/S to the poles; suns rays strike very indirectly over a broad area, therefore these areas are always cold, bitterly cold in winter.