Presentation on theme: "Unit 4: Sun-Earth Relationships"— Presentation transcript:
1Unit 4: Sun-Earth Relationships RevolutionRotationDeclination (Tilt of Earth’s Axis)SeasonsTime ZonesInsolation and its variationSunrise over the Earth. Source:
2OBJECTIVES Examine the Earth’s motions relative to the Sun Demonstrate the consequences of the Earth’s axis tilt for the annual march of the seasonsIntroduce the time and spatial variations in solar radiation received at surface locations
3Revolution of the Earth around the Sun Perihelion-closest to Sun Jan. 3rdAphelion-farthest from Sun July 4thDistance differences from Sun do not influence amount of solar energy received significantlyEarth revolves around the Sun in an elliptical path. Earth and Sun are not drawn to scale, and the orbit’s elongation is highly exaggerated for clarity.
5Declination of the Earth’s Axis Constant tilt of 23.5 degreesProvides seasonsVideo shows misconceptions about the cause of the seasons.
6Midnight Sun: Within the Arctic and Antarctic Circle the Sun does not set at Summer Solstice
7Solar altitude-Sun’s height above the horizon Vertical (90o) Sun is at the equator on equinoxesVertical Sun is at the Tropic of Cancer on summer solsticeVertical Sun is at the Tropic of Capricorn on winter solstice
11Intensity of SunlightSource:Reception of solar radiation at different latitudes showing direct, indirect rays
12Relationship between solar noon altitude and daylight hours Daylength (left axis) and noon solar altitude (right axis) at 45° north latitude. These factors work together in producing pronounced seasonality at middle and high latitudes. Notice also how the pace of change in both is much greater near the equinoxes than near the depths of summer and winter.
13Values of seasonal differences of time and space
14Spatial distribution of insolation at top of the atmosphere as percentage of global average Verify we have permission for this imageSeasonal and spatial variation in solar radiation reaching the top of the atmosphere as a percentage of the global average. The latitude axis is scaled to acount for shrinking area at higher latitudes. Compare with patterns of the previous figures to see how solar position modulates the effect of daylength.