The Motions of the Earth

1. The Motions of the Earth Evidence of Movement and the Consequences

2. How do we know that the Earth is Round? • First, the sky is curved. This is a reflection of the Earth’s curvature. • We can see the Earth’s shadow during a lunar eclipse. • Different constellations are visible in Southern Hemisphere than here. • Sun’s height changes with latitude.

3. Lunar Eclipse:Earth’s shadow on the Full Moon

4. We see different constellations than South Africa

5. The closer to the equator you are, the higher the sun is in the sky. The Sun’s rays are most direct on the equator, and most slanted in polar regions.

6. Rays on Sun on Earth

7. Paths of Sun Across the Sky 0 °lat. 43 °N lat 80 °N lat east south west

8. What proof is there that the Earth rotates in 24 hours? • The Sun, the Moon, the Planets, and the “fixed” stars all move from east to west. • The stars leave trails across the sky that go around the celestial poles. • Physical evidence comes from the Foucault pendulum. • When it’s noon here, it’s midnight in Japan.

9. Star Trails With PolarisNear the Center 20° 33°

10. Similar Pattern in theSouthern Hemisphere …except in the opposite direction to the North! South Celestial Pole

11. Foucault Pendulum All dominoes fall down in a 24 hour period.

12. 6 PM Different Time Zones: one of the results of Earth’s rotation North Pole 12 noon 12 Mid 6 AM

13. 43rd Parallel PortsmouthRochester MuskegonMadison

14. The farther west you go, the later the sun rises and sets. Solar noon is later too.

15. Sundial - Tracking the Sun What is wrong with this picture? (It’s not the watch!)

16. Time Zone Maps

17. The Earth’s Revolution!

18. How do we know that the Earth revolves around the Sun in 365 days? • The Sun completes one trip “through” the zodiac in one year. • The sky looks the same on Sept. 23, 2010 as it did on Sept. 23, 2009. • The sun returns to the same place at the beginnings of each season, which can easily be marked.

19. The Sun appears to move through the 12 signs of the Zodiac in one year cycle. Animation

20. Orion dominates our southern sky every February.

21. For centuries people have marked sun rise positions for midsummer and midwinter.

22. The Sun Dagger • In Chaco Canyon, New Mexico, there is a rock painting aligned with the equinoxes and solstices. • This gave the Anasazi people a way to check their calendar and make corrections as needed. • Other cultures had similar monuments to help them keep track with the yearly cycle of the sun.

23. The Effects of the Earth’s Tilt • The Earth tilts 23.5° but it always points toward the North Star (Polaris). • Because the two poles tilt in the opposite direction, seasons are reversed in Northern and Southern Hemispheres. • The height of the Sun changes with the seasons. • Length of daylight is long in summer and short in winter. Seasons Animation

24. The poles always point in the same direction, which means the Earth either leans toward the sun or away from it.

25. Seasons are reversed in the two hemispheres summer winter winter summer

26. The higher the sun’s path, the higher the intensity… WINTER SUMMER

27. Here in Rochester, the Sun is high in the sky in summer, and low in winter. (The top of the sky is 90°)

28. If you live in Arctic or Antarctic regions the effect of the tilt is even greater Alaska Rochester

29. In Alaska, days are verylong in summer, and veryshort in winter. The same is true for Antarctica.

30. For locations in the Southern Hemisphere, the seasons are reversed, so Dec. 21st is the longest day, and June 21st is the shortest.

31. The Earth’s Precession The Earth slowly wobbles like a top…once every 26,000 years.

32. By an incredible coincidence, Polaris is almost directly over the North Pole. So it can be used to help us navigate. This is a temporary situation, however. Since the Earth is wobbling like a top, the pole slowly moves. This is called precession.

33. The Precession Cycle Now the North Celestial Pole is near Polaris (off by about 1 degree). In the days of the Egyptian pharaohs, it was near Thuban in Draco. In around 12,000 years the wandering pole will point toward Vega, but there will be centuries when there is no North Star.

34. Quick Quiz… • How do we know the earth is round? • What proof do we have that the Earth rotates once every 24 hours? • If we lost all our calendars, how could we determine the length of a year? • Why are seasons reversed in the southern hemisphere from the northern hemisphere? • What is meant by precession? What does that have to do with Polaris?