Page 92 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

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uring the year, places on Earth outside of the equatorial region experience a gradual shift in
daylength by a few minutes each day, and the Sun’s altitude increases or decreases a small amount. Changes in daylength and the sun’s altitude produce changes in insolation that drive weather and climate. Taken together, these changes in Earth’s relationship to the Sun produce the annual “march” of the seasons.
Midnight Sun over Arctic Ocean, June [Bobbé Christopherson.]
2.1 EARTH’S ORIENTATION AT SOLSTICES AND EQUINOXES
The illustration below shows side views of Earth as it appears at the solstices and equinoxes. As Earth orbits the Sun, the 23.5° tilt of Earth’s axis remains constant. As a result, the area covered by the circle of illumination changes, along with the location of the subsolar point (the red dot in the diagrams).
San Juan Mountains, Colorado
Inland, midlatitude locations often have a strong seasonal contrast between summer and winter. [(Top) PHB.cz (Richard Semik)/Shutterstock. (Bottom) Patrick Poendl/Shutterstock.]
March 20 or 21 Equinox
The North and South poles are at the very edge of the circle of illumination. At all latitudes in between, day and night are of equal length.
June 20 or 21 Solstice
At the North Pole, Earth’s axis points toward the Sun, bringing areas above the Arctic Circle within the circle of illumination.
December 21 or 22 Solstice
At the North Pole, Earth’s axis points away from the Sun, excluding areas above the Arctic Circle from the circle of illumination.
23.5°
23.5°
Describe: What is the orientation of Earth’s axis with respect to the Sun on the March equinox?
23.5°
23.5°
Subsolar point at 0° (Equator)
23.5°
Subsolar point at 23.5°N (Tropic of Cancer)
September 22 or 23 Equinox
The North and South poles are at the very edge of the circle of illumination. At all latitudes in between, day and night are of equal length.
Subsolar point at 23.5°S (Tropic of Capricorn)
Sun
23.5°
23.5°
23.5°
Subsolar point at 0° (Equator)
Visit the Study Area in MasteringGeographyTM to explore Geosystems in Action.
Visualize: Study a geosciences animation of the Assess: Demonstrate understanding of Earth–Sun Earth-Sun relations. relations (if assigned by instructor).
geosystems in action 2 EARTh – SUN RELATIoNS
Equator
Equator
Equator
Equator
Arctic Circle Tropic of Cancer
Arctic Circle Tropic of Cancer
Tropic of Capricorn
Tropic of Capricorn
Arctic Circle Tropic of Cancer
Arctic Circle Tropic of Cancer
Tropic of Capricorn
Tropic of Capricorn
Antarctic Circle
Antarctic Circle
Antarctic Circle
Antarctic Circle
N
N
S
S
N
S
N
S