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Astronomy Motions of the Earth and Sun

This review book topic covers the apparent motions of celestial objects, including stars and the sun. It explores the Earth's rotation and revolution, star arcs and daily motion, and the seasons caused by the Earth's tilt.

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Astronomy Motions of the Earth and Sun

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  1. AstronomyMotions of the Earth and Sun Review book topic 4 Pages 60-70 Mrs. Cohn

  2. Apparent Motions of Celestial Objects • Stars in the Night Sky appear to move EastWest • This apparent motion is caused by Earth’s rotation (time it takes earth to spin in 24 hrs). • NOT revolution (time it takes earth to orbit around the sun-365 days)

  3. Star Arcs and Daily Motion • Stars near the north star (polaris) appear to move in complete circles in 24 hours • Parts of a circle are called an “arc” • All motions of stars occur at 15º/hour

  4. Arcs Continued • If each one of these arcs (star paths) were measured to be 60 degrees from the center, how many hours represents this time elapsed photo…? If each arc is 60 degrees, and Earth’s ROR is =15/hr, Than 60 degrees/15 hr yields a 4 hour time elapsed photograph! How many degrees would a star Arc measure at an exposure of 2 Hours? 2 hours x 15/hr= ________

  5. The view of an arc changes with your horizon(N, S, E, W)

  6. Polaris and Earth’s Axis • Earth’s tilt & orientation stay the same as it orbits Sun • Axis always points to Polaris

  7. Towards which direction must be looking to see these star arcs?N, S, E, W? 2. What star is at center? 3. Caused by Earth’s Rotation or Revolution? 59

  8. Star paths and polaris Polaris *remains “fixed” in the night sky *All other stars will move east to west

  9. YouTube star trails in Nevada Q: What direction are we looking at various locations in the video?

  10. Part II: INSOLATION and the Seasons The Electromagnetic Energy (visible and invisible light) that reaches the earth (Incoming-SOLar-radiATION) http://www.learner.org/resources/series28.html

  11. Apparent Motions of the Sun in the Northern Mid-Latitudes • Our own star, the sun also moves through our sky from EastWest at 15º/hour • From Sunrise (E) to Sunset (W), the sun’s path also has the shape of an arc

  12. Our own Star’s path…

  13. To an observer, the sun’s path makes an arc over the course of a day

  14. Questions to discuss: 1.) What causes the seasons? 2.) What causes locations of different latitudes to experience different annual average temperatures? (Why are polar regions colder, and tropical regions warmer?) Facts to consider: 1.) The NH isfurther from the sun in our summer 2.) All areas on earth receive the same daylight hours at the end of a cumulative year

  15. The sun’s path changes in length and position (angle) over the course of a yearLet’s see why…

  16. Caused by Earth’s _____________ around the _____ . Seasonal Motions of the Sun

  17. Summer Solstice (June 21) • Direct sun over Tropic of Cancer • Longest day (in N. Hemisphere) • N. Hemisphere tiled TOWARD sun

  18. Winter Solstice (December 21) • Direct sun over Tropic of Capricorn • Shortest day, Sun tiled AWAY from N. Hemisphere

  19. Vernal Equinox (~March 21) & Autumnal Equinox (~Sept. 21) • Direct sun over Equator (0º) • Equal day and night everywhere

  20. Again, in summary • Due to Earth’s revolution around the sun, and tilt on its axis the sun’s path across the sky changes throughout the year How? • It gets higher and lower in the sky • The Length of path changes (length of day)

  21. Changes in Sun’sAltitude(angle above horizon) Increases or starts getting higher in the sky after Dec. 21 (Winter Solstice) to June 21 when highest (Summer Solstice) Decreases or starts getting lower on June 21  and is lowest on Dec. 21

  22. Summer Solstice • Sun at highest altitude • Sunrise/set NORTH of Due East-West

  23. Vernal (Spring) & Autumnal Equinoxes • Sun at middle altitude • Sunrise/Sunset due East-West

  24. Winter Solstice • Sun at lowest altitude • Sunrise/set SOUTH of due East-West

  25. Let’s Look at what the sun’s path looks like at other Latitudes in the celestial sphere model… • Sun's path interative...click here! Let’s Look at what the sun’s path looks like in the SKY as the seasons change in NY…. Sun's path in the sky interactive animation

  26. Equator

  27. North Pole

  28. Southern Hemisphere at 42 S

  29. Seasonal Change in Temperature is Affected by: 1.) A locations angle of insolation: -higher angles = more concentrated light/ more heating -lower angles= less concentrated light/less heating 2.) The length of day, or Duration of Insolation -Longer days= more time available to heat the surface -Shorter days= less time available for heating

  30. 2.)Duration of Insolation (sunrise  sunset) Key Concept: Any location receives the most heat when the sun is highest in the sky and when the duration is the longest (longer days) *Duration varies with seasons and Latitude

  31. Insolation intensity varies with latitudes:As your distance from the equator increases, insolation concentration decreases

  32. Activities for this section • Page 62-63 # 1-14 in review book (HW) • Skills Sheets Review • Sun’s path Lab with globes • Shadow Length and Direction Activity

  33. Shadow length prediction activity • Note: • The southern hemisphere experiences everything OPPOSITE in terms of the sun’s path • We mean that the sun is at the highest altitude and longest path in the sky on December 21st and the lowest, and shortest path on June 21st

  34. Models that Explain Celestial Motions : Geocentric vs. Heliocentricpg. 63-66

  35. 1.) Geocentric Model – people thought Earth was the center of the universe, and all planets and stars moved in orbits around Earth -first proposed by Aristotle (384-322 BC) -explained observations of: *sunrise/sunset, *moonrise/moonset *and other movements of star paths -because they were thought to rotate around Earth -COULD NOT EXPLAIN the behavior of a pendulum…!

  36. 2.)Heliocentric Model *Sun is at the center of the solar system -and all the planets and comets move around the sun Proposed by Copernicus (1473-1543) Stars remain fixed in the sky but because earth rotates around the sun, these constellations appear to move throughout the year

  37. Evidence of Earth’s Rotation 1. Foucault PendulumFreely swinging pendulum whose path appears to change.

  38. Foucault’s Pendulum : Evidence for Earth’s rotation The ball swings back and forth, knocking the pegs over. It will also move in a circle as the Earth rotates at 15degrees/hour.

  39. 2. Coriolis EffectDeflection of moving particles (ex., wind) to right in N. Hemisphere http://www.youtube.com/watch?v=_36MiCUS1ro http://www.youtube.com/watch?v=mcPs_OdQOYU&feature=related

  40. The prime meridian SUNLIGHT A standard time zone is 15° wide. A time meridian 3. Day & Night (sunrise, sunset)

  41. Evidence for Earth’s Revolution Earth Revolves Counterclockwise • 1 revolution = 365.26 days (1 year)

  42. Evidence of Earth’s Revolution 1. Changing Seasons

  43. 2. Changing Length of Day

  44. Evidence of Earth’s Revolution 3. Changing Constellations

  45. Complete Review Questions • Page 68 in review book # 21-27 21.) 22.) 23.) 24.) 25.) 26.) 27.)

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