© 2007, John Wiley and Sons, Inc. Physical Geography by Alan Arbogast Chapter 3 Earth-Sun Geometry Lawrence McGlinn Department of Geography State University

© 2007, John Wiley and Sons, Inc.

Physical GeographyPhysical Geographyby Alan Arbogastby Alan Arbogast

Chapter 3Chapter 3

Earth-Sun Geometry

Lawrence McGlinnDepartment of GeographyState University of New York - New Paltz


Earth-Sun RelationshipEarth-Sun Relationship

Most Physical Processes on Earth powered by incoming radiation from Sun

Earth-Sun Relationship Complex – Depends on:– Latitude– Position of Sun in Sky– Time of Year– Earth’s Rotation/Axial Tilt


Our Place in SpaceOur Place in Space

Speed of Light299,792 kmps (186,282 mps)Milky Way Galaxy – 100,000 ly acrossOur Solar System – 11 ly acrossMoon is 1.28 light seconds awayGravity – mutual attracting force exerted by

the mass of an object on all other objects


The SunThe Sun

About 4.6 Billion Years Old

Average Star, Nothing Special

100 times diameter of Earth

Powers most natural processes on Earth

8.3 min. for Sun’s energy to reach Earth

Strong Magnetic Fields/Sunspots


Shape of the EarthShape of the EarthInsolation

Variation in Sun Angle by Latitude

Oblate Spheroid

Subsolar Point


At high latitudes, incoming solar radiation is spread over a larger area than at low latitudes, so energy per unit area is relatively low.


Diffuse vs Direct Radiation


Atmospheric Beam DepletionAtmospheric Beam Depletion

Solar radiation is

diminished relative to

the amount of

atmosphere the

radiation passes

through.

High solar angles

see little reduction in

intensity as the path

from the top of the

atmosphere to the

surface is short.


Solar Activity and Solar WindSolar Activity and Solar Wind Solar wind = clouds of electrically charged

particles Sunspots are caused by magnetic storms. These

cause changes in the solar output Sunspots have activity cycles


AurorasAuroras


AurorasAuroras


Earth’s Orbit Around the SunEarth’s Orbit Around the Sun

Plane of the Ecliptic

One Revolution = 365.24 Days

Elliptical Orbit

Perihelion/Aphelion

Seasons not due to distance from Sun


S

The Earth follows an elliptical orbit around the Sun with its closest point at Perihelion and its farthest point at aphelion

Aphelion and Perihelion


Viewed from above the North Pole, the Earth’s rotation and revolution are both counterclockwise.

S

E


Physical GeographyPhysical Geographyby Alan Arbogastby Alan Arbogast

Chapter 3Chapter 3

The Seasons

Lawrence McGlinnDepartment of GeographyState University of New York - New Paltz


Dimensions and DistancesDimensions and DistancesEarth’s orbit

– Average distance from Earth to the Sun is 150,000,000 km (93,000,000 mi)

– Perihelion – closest at January 3 147,255,000 km (91,500,000 mi)

– Aphelion – farthest at July 4 152,083,000 km (94,500,000 mi)

– Takes energy 8 min 20 sec to reach Earth– Plane of Earth’s orbit is the plane of the

ecliptic


The Seasons The Seasons

Seasonality: the variation of the sun’s position over the horizon; the changing daylength during the year

Seasons result from: variations in the sun’s altitude, the suns’s declination, and daylength, WHICH are dependent upon……


Reasons for Seasons Reasons for Seasons

Revolution– Earth revolves around the Sun– Voyage takes one year, roughly– Earth’s speed is 107,280 kmph (66,660 mph)

Rotation– Earth rotates on its axis once every 24 hours– Rotational velocity at equator is 1674 kmph

(1041 mph)


Reasons for Seasons Reasons for Seasons

Tilt of Earth’s axis– Axis is tilted 23.5° from plane of ecliptic

Axial parallelism– Axis maintains alignment during orbit around

the Sun– North pole points toward the North Star

(Polaris)

Sphericity


The Earth’s tilt and orientation hold steady as it orbits the Sun.


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°

N


Solstice and EquinoxSolstice and Equinox

Fall Equinox (Sept 22-23)– Subsolar Point – Equator

Winter Solstice (Dec 21-22)– Subsolar Point - Tropic of Capricorn –

23.5° S


Tropic of

Capricorn

Tropic of

Cancer

Equator

Tropic of

Capricorn

Tropic of CancerEquator

Tropic of

Capricorn

Tropic of

Cancer

Equator

Tropic of

Capricorn

Tropic of

Cancer

Equator


Range of seasonal movement of subsolar point

Tropic of Capricorn

Tropic of Cancer

Equator


Solar declination: latitudinal change ofatitudinal change of subsolar pointssubsolar points


Sun’s ArcSun’s Arc

© 2007, John Wiley and Sons, Inc.The Sun as seen from 45°N in June and in December.

Sun’s ArcSun’s Arc


Seasonal ObservationsSeasonal Observations


Seasonal ObservationsSeasonal Observations

SUMMER HEMISPHERE

Carrollton = 33°

What is Sun’s angle (at noon) on June 21?

90 – |(latitude – subsolar point)|

90 – |(33 – 23.5)| = 80.5 °

WINTER HEMISPHERE

90 – (latitude + subsolar point)


Annual March of the SeasonsAnnual March of the Seasons

Winter solstice – December 21 or 22– Subsolar point Tropic of Capricorn

Spring equinox – March 20 or 21– Subsolar point Equator

Summer solstice – June 20 or 21– Subsolar point Tropic of Cancer

Fall equinox – September 22 or 23– Subsolar point Equator


Annual March of the SeasonsAnnual March of the Seasons

Documents

© 2007, John Wiley and Sons, Inc. Physical Geography by Alan Arbogast Chapter 3 Earth-Sun Geometry Lawrence McGlinn Department of Geography State University