1. Earth, Sun, Moon and the Seasons Topic 4 and 6 Discussion Question Review Question

2. Actual Motions of the Earth Completes 1 rotation in 24 hrs – 15  /hour Spins on an imaginary line called an axis – Runs through poles – Axis is tilted  Completes 1 revolution in 365 days  ~ 1  /day  Revolves around the Sun  Perihelion = closest to the Sun  Aphelion = further from the Sun Animation

3. Celestial Sphere An imaginary sphere with a very large radius The earth is located at the center of the sphere Poles of sphere along with the poles of Earth

4. Apparent Motion of Celestial Objects Celestial object: A natural object that is located outside of Earth’s atmosphere – Stars, Planets, Moons Appear to move across the sky – Result of Earth’s motions – travels E to W Daily @ 15  /hr – Yearly motions result of Earth’s revolution Apparent Motion: illusion in which a stationary object appears to move Why do celestial objects appear to travel at a rate of 15  /hr across our sky?

5. Apparent Motion of Celestial Objects Celestial Object MotionPosition Description Planets - Daily E  W 15  /hr - “Eastward amongst stars” - All planets revolve around the Sun - Some revolutions are slower than Earth’s - Retrograde Motion: Planets sometimes appear to make loops and move back (western among stars) Sun - Daily E  W 15  /hr - Forms an Arc -Length of path changes daily -Lowest position at sunrise and sunset -Reaches highest pt at Local Solar Noon - Altitude depends on LAT and time of year -Greater length of Arc = More Sunlight -Summer = Longest path -Winter = Shortest path Moon - Daily E  W 15  /hr - Rises 50 mins later each day - Moon has to “catch up” to Earth’s revolution - Moves “eastward amongst stars” - Cyclic and predictable Animation Sun's Path and Latitude Sun's Path and Latitude

6. Daily Path of the Sun Only between 23.5  N and 23.5  S can the noon sun be directly overhead at 90  angle (Zenith) Path of the Sun

7. Solar Noon The time of day when the Sun is at its highest altitude in the sky Altitude of Solar Noon changes daily – Depends on latitude and season – Cyclic event Sunrise photos taken at same local 3x in the year North of East Due East South of East Is solar noon at the same time as clock noon each day?

8. Determine the Noon Angle of the Sun 1.Determine the location’s latitude. 2.Determine its difference from latitude when noon Sun is at the Zenith (90 °). 3.Subtract difference from 90. Example: Location’s Latitude = 35 o NDate: June 21 st Difference from Tropic of Cancer (35 - 23.5) = 11.5 o Angle of Noon Sun (90 – 11.5) = 78.5 o

9. LocationDateAltitude of the Noon Sun 0°0° Winter Solstice66.5° Equinoxes90° Summer Solstice66.5° 90° N Winter SolsticeNot visible Equinoxes0°0° Summer Solstice23.5 90° S Winter Solstice23.5 Equinoxes0°0° Summer SolsticeNot visible 23.5° N Winter Solstice43° Equinoxes66.5° Summer Solstice90°

10. LocationDateAltitude of the Noon Sun 23.5° S Winter Solstice90° Equinoxes66.5° Summer Solstice43° 41° N Winter Solstice25.5° Equinoxes49° Summer Solstice72.5° 30° S Winter Solstice83.5° Equinoxes60° Summer Solstice36.5°

11. At our Latitude (41  N) SeasonFirst DayPosition of Arc Summer Solstice~ June 21 st - Sun rises & sets N. of E - Longest path Autumn Equinox~ Sept. 23 rd - Sun rises & sets due E - Middle Path Winter Solstice~ Dec. 21 st - Sun rises & sets S. of E - Shortest path Vernal (Spring) Equinox ~ March 21 st - Sun rises & sets due E - Middle Path Interactive Why does the altitude of the noon Sun differ by 23.5°?

12. Direction of sunrise and sunset changes during the year What is “Manhattanhenge” and when does this happen?

13. INSOLATION Portion of the Sun’s radiation that reaches Earth’s surface Amount varies depending on Latitude and Season (Cyclic) INcoming SOLar radiATION = Intensity of Insolation - Rate at which solar energy is received by a given area per time Angle of Insolation - Angle at which solar energy reaches Earth - Higher angle = greater intensity - Only locations between 23.5 N and 23.5 S receive a 90 degree noon sun angle at some point during the year Duration of Insolation - Amount of time that sunlight is reaching Earth’s surface - Greatest in Summer, least in Winter -Always 12 hrs at equator -Polar regions have greatest yearly Range (0-24 hours)

14. Which number shows Earth at perihelion position? The aphelion position? 1 4 2 3

15. Interactive

16. - Lowest Angle - Lowest Intensity - Shortest Duration - Highest Angle - Highest Intensity - Longest Duration Animation At our latitude (41  N) During which month is the longest day of the year in NYC? The shortest? How long is the duration of Insolation for each day?

17. Maximum duration in NY (15 hours) on summer solstice. Average duration (12 hours) on equinoxes. Least duration in NY (9 hours) on winter solstice. Animation At our latitude (41  N) **Most amount of hours during summer** **Least amount of hours during winter** **Most amount of hours during summer** **Least amount of hours during winter**

18. Factors affecting Absorption and Reflection In Atmosphere – Ozone (0 3 ) absorbs UV (ultraviolet) light – Clouds and Aerosols reflects and scatters insolation Examples of Aerosols: ice crystals, water droplets, dust, bacteria, volcanic ash On Earth’s Surface – Land: better absorber and radiator – Water: better reflector of sunlight – Ice/snow: reflect radiation Describe a surface that would absorb insolation? Reflect insolation?

19. Why do we have seasons? Result from cyclic variations of the angle of insolation and the intensity and duration of insolation that occurs during the year Generally follows the north-south shift in the direct rays of insolation – Caused by tilt of Earth’s axis occurs between 23.5  N and 23.5  S Video What can you infer this to mean based on the word cyclic?

20. Reasons for the seasons The Tilt of Earth’s axis Parallelism of axis Revolution of Earth

21. The Tilt of Earth’s axis Earth’s axis is tilted 23.5  Angle of the tilt determines the intensity of the seasons Parallelism of the Axis – The tilt is always pointed in the same direction regardless of its position in its orbit Results of Angle and Parallelism – Angle of insolation varies based on location on Earth – Duration of insolation varies throughout the year AngleIntensityResults Greater than 23.5  Greater- Warmer Summers - Cooler Winters Less than 23.5  Less- Cooler Summers - Warmer Winters

22. Parallelism of the Axis Earth’s Axis points in the same direction in space at all location in its orbit around the sun

23. Earth’s Revolution around the Sun The Earth travels along a cyclic path around the Sun Earth’s tilt is not always pointed towards the Sun – Varies due to Parallelism of the Axis

24. Significant Dates DateNameSignificance December 21 st Winter Solstice -First day of winter - N. Pole tilted away from the Sun - Direct sunlight @ Tropic of Capricorn (23.5  S) - Southern Hemisphere experiences greater duration of insolation March 21 st Vernal Equinox -First day of spring - Earth not tilted towards Sun - Direct sunlight @ the equation (0  ) - Equal duration of insolation June 21 st Summer Solstice -First day of summer - N. pole tilted toward the Sun - Direct sunlight @ Tropic of Cancer (23.5  N) - Northern Hemisphere experiences greater duration of insolation September 23 rd Autumnal Equinox -First day of fall (autumn) - Earth not tilted towards Sun -Direct sunlight @ the equator (0  ) - Equal duration of insolation

25. Animation Explain why the N. Pole does not receive any sunlight for 6 months?