• Revolution

• Rotation

• Declination (Tilt of Earth’s

Axis)

• Seasons

• Time Zones

• Insolation and its variation Sunrise over the Earth. Source: http://ajorbahman.blogspot.com/2011/02/third-of-russians-think-sun-spins-round.html

Unit 4: Sun-Earth Relationships

OBJECTIVES• Examine the Earth’s motions relative to

the Sun• Demonstrate the consequences of the

Earth’s axis tilt for the annual march of the seasons• Introduce the time and spatial

variations in solar radiation received at surface locations

Revolution of the Earth around the Sun

• Perihelion-closest to Sun Jan. 3rd

• Aphelion-farthest from Sun July 4th

• Distance differences from Sun do not influence amount of solar

energy received significantly

Earth 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.

Counterclockwise movements

• Revolution-annual cycle

• Rotation-daily cycle

Declination of the Earth’s Axis• Constant tilt of 23.5 degrees• Provides seasons

Video shows misconceptions about the cause of the seasons. http://www.youtube.com/watch?v=iMEfYLvxioc

Midnight Sun: Within the Arctic and Antarctic Circle the Sun does not set at

Summer Solstice

Solar altitude-Sun’s height above the horizon

• Vertical (90o) Sun is at the equator on equinoxes

• Vertical Sun is at the Tropic of Cancer on summer solstice

• Vertical Sun is at the Tropic of Capricorn on winter solstice

March of the Seasons

World’s Time Zones

Why are the boundaries not straight lines?Why are the Prime Meridian, International Dateline significant?

Source: http://www.colourbox.com/vector/clocks-in-people-head-vector-invitation-card-vector-3095601

Daylight hours by dates and latitudes

Intensity of Sunlight

Reception of solar radiation at different latitudes showing direct, indirect rays

Source: http://nsidc.org/cryosphere/frozenground/what_affects_fg.html

Relationship 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.

Values of seasonal differences of time and space

Spatial distribution of insolation at top of the atmosphere as percentage of global average

Verify we have permission for this image

Seasonal 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.