1. 4/23/2017
What is Earth’s shape?
Is it flat like a coin, or spherical like a ball? Perhaps it’s like a tin can, flat on the ends and round in the middle?
Describe the evidence that best supports you answer.

2. 4/23/2017
Spherical Earth?
Scientists claim that Earth is much like a slightly flattened ball - an oblate spheroid.
How do they know or do the merely have faith in the claim?
What is the evidence that supports a scientific belief in a roughly spherical Earth?

3. Ships appear to sink gradually below horizon from bottom up.
4/23/2017
Ships appear to sink gradually below horizon from bottom up.

4. 4/23/2017
Polaris, the North Star
Polaris
is located practically over the North Pole of planet Earth.
If you stood at the North Pole, Polaris would be almost directly overhead.

5. Why do observations of Polaris help determine Earth’s shape?
4/23/2017
Why do observations of Polaris help determine Earth’s shape?
The North Star gradually appears lower and lower in the sky as you travel toward the equator.
When the North Star is visible at the horizon, you are located at the equator.
South of the equator the North Star is not visible at all.
These observations are possible only for a roughly spherical Earth.

6. 4/23/2017
Lunar Eclipses
Only a sphere can cast a shadow that always appears round. During lunar eclipses, Earth casts its shadow on the moon and the shadow is always round.

7. 4/23/2017

8. Many other indications…
Circumnavigation of the globe.
Existence of time zones.
Earth-orbiting satellites.
Photographs from space.
Eyewitness reports of astronauts.
Other objects - sun, moon, planets - are roughly spherical.

9. Summary: How do we know the Earth to be spherical?
4/23/2017
Summary: How do we know the Earth to be spherical?
Ships appear to sink GRADUALLY below the horizon as they travel away from observer and over the horizon - in all directions.
Polaris (North Star) changes altitude (angle measured in degrees above earth’s surface) with latitude – at all longitudes.
Lunar Eclipses - Earth’s shadow on the moon is always round.
Satellite imagery and much more.

10. Is Earth perfectly spherical?
4/23/2017
Is Earth perfectly spherical?
The Earth is NOT a perfect sphere
It is flattened at the poles and bulges at the equator due to its spinning.
Earth is very slightly out of round or OBLATE.
Saturn is an even better example of being oblate.

11. What proof is there that the Earth is slightly oblate?
4/23/2017
What proof is there that the Earth is slightly oblate?
Gravity measurements. Gravity is the force of attraction between any two objects Increase mass of objects = increase gravity Decrease distances = increase gravity
If Earth were a perfect sphere, it would be expected to exert an equal force on objects at equal distances from the center of earth.

12. The pull of gravity is weaker farther from the center of Earth
4/23/2017
The pull of gravity is weaker farther from the center of Earth
You weigh just a bit less at the equator than at the pole!

13. The Oblate Sphere The difference with a sphere is small
4/23/2017
The Oblate Sphere
The difference with a sphere is small
We can not see it with the naked eye
Earth still appears like a sphere

14. Why is Earth not perfectly round?
4/23/2017
Why is Earth not perfectly round?
Earth’s spinning (rotation) causes…
bulging at equator and
flattening at the poles.
Be careful on multiple-choice tests!

15. A look at our nearest neighbor in Space!
The Moon
A look at our nearest neighbor in Space!

16. What is the Moon? A natural satellite
One of more than 96 moons in our Solar System
The only moon of the planet Earth

17. Location, location, location!
About 384,000 km (240,000 miles) from Earth
3,468 km (2,155 miles) in diameter (about ¼ the size of Earth)

18. Birth of the Moon “Born” 4-5 billion years ago
Formed from impact of Mars-sized “planetesimal” on Earth
Debris from both objects melted together to form the Moon

19. Movements of the Moon
Revolution – Moon orbits the Earth every 271/3 days
The moon rises in the east and sets in the west
The moon rises and sets 50 minutes later each day
Rotation – Moon turns on its axis every 27 days
Same side of Moon always faces Earth

20. It’s Just a Phase Moonlight is reflected sunlight
Half the moon’s surface is always reflecting light
From Earth we see different amounts of the Moon’s lit surface
The amount seen is called a “phase”

21. Waxing and Waning New moon Waxing Crescent moon First Quarter moon
Waxing Gibbous moon
Full moon
Waning Gibbous moon
Third Quarter moon
Waning Crescent moon

22. FOUR MAIN SHAPES
FULL
Four Basic Shapes
CRESCENT
GIBBOUS
QUARTER

24. Lunar Eclipses
Moon moves into Earth’s shadow – this shadow darkens the Moon
Umbra
Penumbra
About 2-3 per year
Last up to 4 hours

25. Solar Eclipses Moon moves between Earth and Sun
Moon casts a shadow on part of the Earth
Total eclipses rare – only once every 360 years from one location!

26. The Tides Tides caused by pull of Moon’s gravity on Earth High tide –
Side facing Moon and side away from Moon
Every 12 hours, 25 ½ minutes
Low tide –
On sides of Earth