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© 2007, John Wiley and Sons, Inc.
Physical GeographyPhysical Geographyby Alan Arbogastby Alan Arbogast
Chapter 3Chapter 3
Earth-Sun Geometry and the Seasons
Lawrence McGlinnDepartment of GeographyState University of New York - New Paltz
© 2007, John Wiley and Sons, Inc.
Earth-Sun RelationshipEarth-Sun RelationshipMost Physical Processes on Earth powered by
incoming radiation from Sun
Earth-Sun Relationship is Complex – Depends on:– _____________– _____________– _____________– _____________
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Our Place in SpaceOur Place in Space
Big-Bang Theory
Milky Way Galaxy
Our Solar System
Milky Way GalaxyMilky Way Galaxy
Figure 2.1
Our Solar SystemOur Solar System
Figure 2.1
Dimensions and distancesDimensions and distances
Speed of light– __________________________– Universe is _____________ across– Milky Way Galaxy _____________– Our Solar System _____________ across from
Earth’s perspective– Moon is _____________away
Earth’s OrbitEarth’s OrbitAverage distance from Earth to the Sun is _______________________________________ – closest at _____________–_______________________________________ – farthest at _____________–__________________________
Earth is __________________from the SunPlane of Earth’s orbit is the ______________
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Shape of the EarthShape of the Earth
_____________
_____________ - Earth-shaped object
Variation in Sun Angle by _____________
_____________
Sun Angle & Length of Day
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At high latitudes, incoming solar radiation is spread over a larger area than at low latitudes, so energy per unit area is relatively low.
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The SunThe SunAbout _____________Old
Average Star, Nothing Special
_____________diameter of Earth
Powers most natural processes on Earth
_____________for Sun’s energy to reach
Earth
Strong Magnetic Fields/Sunspots
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Earth’s Orbit Around the SunEarth’s Orbit Around the Sun
_____________
One Revolution = _____________
_____________ Orbit
_____________
_____________
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The Earth follows an elliptical orbit around the Sun with its closest point at Perihelion and its farthest point at aphelion
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The Earth’s Rotation & Axial The Earth’s Rotation & Axial TiltTilt
The Earth’s Rotation around its Axis
_____________ Rotation around North Pole
Circle of Illumination
Earth as Viewed from the Sun
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Viewed from above the North Pole, the Earth’s rotation and revolution are both counterclockwise.
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Global TimeGlobal Time
_____________ Time Zones
Prime Meridian
International Date Line
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Earth’s 24 Time Zones
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The SeasonsThe Seasons
Earth’s tilt 23.5 from perpendicular to Ecliptic
Angle and orientation constant in Orbit
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The Earth’s tilt and orientation hold steady as it orbits the Sun.
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The SeasonsThe Seasons
Tilt and revolution combine to cause seasons– Northern & Southern Hemispheres
alternate direct radiation from the Sun– Subsolar Point migrates between 23.5
degrees N and 23.5 degrees S.
Which of the following latitudes will experience the effects of the sun's subsolar point?
A. 0 degreesB. 20 degrees N and 20 degrees SC. 40 degrees N and 40 degrees SD. Both A and BE. Both B and C
Answer: D
5 Factors That Influence 5 Factors That Influence Seasonal Change Seasonal Change
RevolutionRotationTilt of the earth's axisAxial parallelismSphericity
RevolutionRevolution
Earth revolves around the SunVoyage takes one yearEarth’s speed is 107,280 km/h
RotationRotation
Earth rotates on its axis once every 24 hours
Rotational velocity at equator is 1675 km/h (1041 mph)
Revolution and RotationRevolution and Rotation
Reasons for Seasons Reasons for Seasons Tilt of earth's axis
– Axis is tilted 23.5° from perpendicular to the plane of ecliptic
Axial parallelism– Axis maintains alignment during orbit around
the Sun– North pole points toward the North Star
(Polaris)
Sphericity (geodesy)
Axial Tilt and ParallelismAxial Tilt and Parallelism
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The Earth’s orbit and tilt combine to create the seasons.
Orbital View
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Solstice and EquinoxSolstice and Equinox
Spring Equinox (March 20-21)– Subsolar Point – Equator
Summer Solstice (June 20-21)– Subsolar Point – Tropic of Cancer –
23.5 degrees N
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Solstice and EquinoxSolstice and Equinox
Fall Equinox (September 22-23)– Subsolar Point – Equator
Winter Solstice (December 21-22)– Subsolar Point – Tropic of
Capricorn – 23.5 degrees S
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Earth-Sun Geometry on EarthEarth-Sun Geometry on EarthSun’s Arc across the Sky
Seasonal Changes in Sun Position
The Sun as seen from 45°N in June and in December.
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Earth-Sun Geometry on EarthEarth-Sun Geometry on Earth
Variation in Day Length by Latitude
Variations in Day Length on Equinoxes and Solstices by Latitude.
Where is the subsolar pint as of today?
A. Southern hemisphere, near 23.5 degrees SB. Southern hemisphere, near the equatorC. Northern hemisphere, near 23.5 degrees ND. Northern hemisphere, near the equator
Answer: A
