Measuring Earth

1. Measuring Earth Aim: What is the size and shape of planet Earth? Do Now: How did early scientists discover the size and shape of Earth?

2. Earth’s shape almost resembles a perfect sphere; however… Due to Earth’s rotation in a counter-clockwise (west-to-east) direction, the shape is slightly altered.

3. The north and south poles are slightly flattened. As a result, the equator slightly bulges outward. Slightly Oblate Spheroid

4. Since Earth is slightly oblate, your weight will differ at the same elevation above sea level. Example: Your weight will be greater at the poles than at the equator because of the gravitational force is greater at the poles. Gravimeters: instruments that measure the downward acceleration of gravity.

6. The equatorial diameter is larger than the polar diameter. Diameters Polar: 12,714 km Equatorial: 12,756 km

7. How do you find the roundness ratio of a sphere? If it equals “1”, then the sphere is a perfect circle Polar diameter = Equatorial diameter Roundness Ratio of Earth = 0.9967 The further from “1”, the less spherical the planet is.

8. Which diagram most accurately shows the cross-sectional shape of Earth? (1) (3) (2) (4)

9. Summary Describe why the shape of the earth is not a perfect circle? What term is used to describe the shape of the Earth? Would your weight be the same all around the Earth? Assume that you took your weight at the same elevations.

10. At sea level, where would you be closest to the center of Earth?

11. According to the data table below, what is the exact shape of Earth? Actual Dimensions of Earth Equatorial Radius 6,378 km Polar Radius 6,357 km Equatorial Circumference 40,076 km Polar Circumference 40,008 km (1) Slightly flattened at both the Equator and Poles (2) Slightly bulging at both the Equator and Poles (3) Slightly flattened at the Equator and slightly bulging at the Poles (4) Slightly flattened at the Pole and slightly bulging at the Equator

12. How can modern day scientists and early civilizations determine that the Earth is curved?

13. The best proof of the shape of the Earth is from satellite imagery (modern). There are many other ways to understand Earth’s shape:

14. Tall ships disappearing into the horizon  curved Earth.

15. During a lunar eclipse one can see a curved shadow on the moon.

16. Polaris (North Star): If you travel northward, the star appears to rise above the horizon.

17. Northern Hemisphere can see Polaris, the Southern Hemisphere cannot. Note: The altitude of Polaris is the same as the observer’s latitude. • Manhattan: +/- 41°N; an observer can see Polaris at an angle of 41 degrees from the horizon. • North Pole (Polaris zenith): 90 °N; an observer can see Polaris directly overhead.

19. What would happen if the observer was located at the equator?

20. If you travel east or west on the same latitude, the altitude of Polaris will ________________. remain the same

21. Summary Which of the following is NOT evidence that supports Earth’s spherical shape? (1) Photographs taken from outer space (2) Ships appearing to sink as they sail past the horizon (3) The changing seasons (4) The similarities in gravity at sea level all over Earth

22. To an observer at sea level, at which latitude does the North Star appear closest to the horizon? (1) 5°N (2) 20°N (3) 50°N (4) 85°N

23. Which diagram represents the approximate altitude of Polaris as seen by an observer located in Syracuse, New York?