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Lab 3: Earth Sun-Geometry

Lab 3: Earth Sun-Geometry. Earth’s axis is tilted 23½ ° (from the perpendicular to the plane of the ecliptic) Primary cause for Earth’s seasons! Tilt is oriented in the same direction all year: North Pole points towards Polaris. Earth-Sun Geometry. Solstices : Summer ( June 21 or 22 )

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Lab 3: Earth Sun-Geometry

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  1. Lab 3:Earth Sun-Geometry

  2. Earth’s axis is tilted 23½° (from the perpendicular to the plane of the ecliptic) • Primary cause for Earth’s seasons! • Tilt is oriented in the same direction all year: • North Pole points towards Polaris

  3. Earth-Sun Geometry • Solstices: • Summer (June 21 or 22) • Northern Hemisphere is tilted 23½° toward the sun • Sun’s rays are directly over head at 23½° N (Tropic of Cancer) • Winter (December 21 or 22) • Northern Hemisphere is tilted 23½° away from the sun • Sun’s rays are directly over head at 23½° S (Tropic of Capricorn) Solar Noon = Sun at highest point in the sky

  4. Earth-Sun Geometry http://www.geography.hunter.cuny.edu/~tbw/wc.notes/2.heating.earth.surface/01_EarthSun.html

  5. Equinoxes: • Midway between solstices • Autumnal equinox – September 22 or 23 • Vernal equinox – March 21 or 22 Rotation Animation

  6. Sun angles vary with latitude: • High sun angles in the tropics • Medium sun angles at mid-latitude • Low sun angles in the arctic

  7. Sun Angle by Season

  8. Solar declination: latitude at which the sun is directly above at solar noon (only between 23 ½ N-S) • Zenith angle (ZA): the angle between a point directly overhead & the sun at solar noon (related to the 90 degrees) • Solar elevation angle (SA): the angle of the sun above the horizon at solar noon (relates to 0 degrees)

  9. Finding Zenith • Know where the sun is directly overhead + or – 2. Latitude of location • HINTS: • Locations in same hemisphere = SUBTRACT! • Locations in different hemispheres = ADD! • Solar Declination is 0° = SUBTRACT!

  10. Formulas: 1. Zenith Angle = 90 – Sun Angle 2. Solar Elevation Angle = 90 – Zenith Angle • Location gives you Zenith Angle • Date gives you Solar Declination

  11. Calculating Solar Declination • Use formula: 23.5 * sine (n) OR • Use an Analemma!

  12. June 21: summer solstice (23½ °N) NH tilted towards the sun SD = 23½°N 47° 66.5 – 23.5°(SD) = 43°(ZA) 90° – 43°(ZA) = 47°(SA)

  13. SUN ANGLE: 36½° Heating efficiency of 58.78%

  14. 83½° ZA 8.834 units • Note your latitude! • Determine – • Sun at 90° • ZA (difference between your locations) • SA (90° – ZA) Sun at 90°: 23½° S ZA: 23½° + 60° = 83½° SA: 90° – 83½° = 6½° **units determined by 1/sin(SA) The larger the unit, the cooler the temperature. WHY?

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