Unit III: The Earth in Space

1. Unit III: The Earth in Space

2. Celestial Objects • Any natural object “outside” the earths atmosphere (seen in the sky)

3. Celestial Sphere • The imaginary sphere on which all objects in the sky appear on.

4. How do celestial objects move in the sky? • Apparent Daily Motion: the apparent motion of celestial objects in a path from east to west in the sky over a 24 hour period.

5. Why is it called “apparent motion”? • The objects themselves DO NOT MOVE—the Earth ROTATES (spins) Tractor Trailer Effect

6. Celestial objects appear to move along a curved path called an ARC.

7. Constellations: groups of a few stars that form a pattern in the sky • Examples- Big Dipper, Little Dipper, Orion

9. Models of the Night Sky • Geocentric Model: shows the Earth in the center of the universe and everything else revolving around it. (Earth does not move) THIS IS WRONG!!!!!

10. Heliocentric Model: sun in the center of our Solar System and the Earth and other planets revolving around it. This is Correct!

11. The Heliocentric Model Takes Two Earth Motions Into Account • The Earth rotates (spins) on its axis at a rate of 15° per hour (daily motion)

12. The Earth revolves (orbits) around the Sun at a rate of 1° per day (annual motion)

13. Period of Revolution: amount of time it takes an object to go around the sun once.

14. How do we know that Earth really rotates on its axis? • Foucault Pendulum: swinging weight that is free to rotate as it swings back and forth. As the Earth rotates, the pendulum changes direction.

15. Coriolis Effect: apparent curving of objects to the right in the Northern Hemisphere (counterclockwise spin)

16. How do we know that Earth revolves around the sun? • Seasons • Changing Constellations (at different times of the year you see different constellations)

17. Apparent Motions of the Sun ***The Sun, just like other stars, rises in the east and sets in the west because of Earth’s Rotation

18. Apparent Solar Day: the interval of time during which the Sun passes from its highest point on one day to its highest point on the next.

19. Solar Noon: sun’s highest point in the sky during the day **the Sun’s apparent speed never changes

20. Shadows…. • The higher the sun is in the sky, the shorter the shadow • Shadows occur opposite the sun

21. afternoon morning / evening

22. This shows up all the time!

23. Which direction do the Sun and stars appear to move? • When looking east, west, or south, stars will appear to move to the right Eastern Sky

24. Western Sky

25. When looking north, stars will form circles around Polaris (remember Polaris NEVER moves)

26. Seasons What causes seasons on Earth? • Tilt of the Earth’s Axis of 23 ½ º

27. Parallelism of the Axis: regardless of the Earth’s position the axis always points in the same direction as it revolves

28. ****the cause of the seasons IS NOT DUE to the fact of how close the Earth is to the Sun—in fact the Earth is closest to the Sun in January because of Earth’s elliptical orbit

30. Tropic of Cancer: an imaginary line that is located 23 ½ degrees north of the Equator

31. Tropic of Capricorn: an imaginary line that is located 23 ½ degrees south of the Equator

32. **the Sun will only get directly overhead (Zenith) between the Tropics **the equator always gets 12 hours of daylight!!!

33. Four Important Days in Earth Science: • Summer Solstice: • June 21st • Northern hemisphere is tilted towards the Sun • Insolation (incoming solar radiation) is most direct (sun highest in the sky) • Longest Day of the year in the Northern Hemisphere • Sun is directly above The Tropic of Cancer at noon • Sun rises north of east and sets north of west

34. Summer Solstice

35. Autumnal Equinox • September 23rd • Day and night are equal (Equinox: “Equal Night”) • Sun is directly over the Equator at noon • Sun rises due (exactly) east and sets due west

36. Autumnal Equinox

37. Winter Solstice: • December 21st • Northern Hemisphere is tilted away from the Sun • Insolation is least direct (sun lowest in the sky) • Shortest day of the year in the Northern Hemisphere • Sun is directly above The Tropic of Capricorn at noon • Sun rises south of east and sets south of west

38. Winter Solstice

39. Vernal Equinox: • March 21st • Day and night are equal (Again, Equinox means “equal night”) • Sun is directly over the equator at noon • Sun rises due east and sets due west

40. Vernal Equinox

43. Seasons Review • The tilt (or “inclination”) is the reason for the seasons • Temperature changes because the Sun’s rays strike the earth at different angles (high altitude = high temp.) • Insolation = Sunlight • On the equinoxes, the Sun is directly over that equator at noon • On the summer solstice, the Sun is directly overhead The Tropic of Cancer at noon • On the winter solstice, the Sun is directly overhead The Tropic of Capricorn at noon • The Lower the Sun is in the sky, the longer the shadow • The equator always has 12 hours of daylight

44. **Remember** **The Sun ONLY gets 90° (directly overhead in the tropics (23 ½º N and 23 ½º S)**