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EARTH-SUN RELATIONS

A. INTRODUCTION

• Insolation: incoming solar radiation

• Prime energy source affecting all spheres of the earth's physical environment

• Amount of insolation related to:

  • sun angle

  • day length

  • atmospheric thickness (path length)

Image source: Images from Galileo. NASA/JPL http://www2.jpl.nasa.gov/galileo/images/earth.html

B. EARTH IN SPACE

• Motions: rotation & revolution

• Axial tilt: 23.5^o away from perpendicular to plane of ecliptic

• Parallelism

• Circle of Illumination

C. SUN ANGLE

At a given location, sun angle changes

• throughout the day

• throughout the year

 

On a given date, sun angle changes as latitude changes

declination: latitude where the sun angle is 90o at noon June solstice = 23.5o N; December solstice = 23.5o S March & September equinoxes = 0o (equator)

 

D. LENGTH OF DAY

• Geographic location (latitude)

• Time of year

E. ATMOSPHERIC PATHLENGTH

• Thicker atmosphere = less energy

• Related to sun angle

F. SUMMARY  

• Earth in space: rotation, revolution, axial tilt, parallelism

• Available energy (insolation) function of: sun angle, day length, atmospheric thickness

• Insolation varies geographically and temporally (latitude, time of day, time of year)

• Insolation affects temperature patterns