Sun, Earth and Moon

1. Chapter 11, Section 1
Notes

2. 2 Mistaken ideas about Earth?
• Earth was center of universe
• Earth was considered flat

3. Why did Aristotle suspect the Earth was
spherical?
• He observed that the Earth cast a curved shadow on the Moon during
an eclipse.

4. What observations did sailors make to indicate
the Earth is spherical?
• The tops of approaching ships appeared first on the horizon.
• Studied the night sky (North Star)

5. Is the Earth a perfect sphere?
• No, it bulges slightly at the equator and is somewhat flattened at the
poles.

6. What causes day and night?
• The rotation of the Earth. (spinning on its axis)

7. How long is a complete rotation?
• About 24 hours or 1 day

8. How many rotations in a year?
• About 365 rotations in a year

9. What generates Earth’s magnetic field?
1. Movement of material inside Earth’s core
2. Earth’s rotation

10. What is the purpose of the magnetic field?
• Protects us from harmful solar radiation by trapping many charged
particles from the Sun

11. Magnetic axis vs. Rotational axis
• Earth’s magnetic axis—line joining its north and south magnetic
poles
• Rotational axis—line based on tilt of the Earth
• Earth’s magnetic axis and rotational axis do not line up. A compass
would lead you to magnetic axis.

12. Do magnetic poles change? Why?
• The magnetic poles move around the rotational poles in an irregular
way. This can be significant over decades.

13. What is the shape of the Earth’s orbit?
• Earth’s orbit is an ellipse.

14. When is the Sun closest to the Earth?
Farthest?
• Earth gets closest to the Sun around January 3rd.
• Earth is farthest from the Sun around July 4th.

15. What causes the seasons on Earth?
• The tilt of the Earth is the reason for the seasons.

16. Why is summer warmer than winter?
• 1. the hemisphere tilted toward the Sun receives more hours of
sunlight each day than the hemisphere tilted away from the Sun.
• The tilt also causes the Sun’s radiation to strike the hemisphere at
different angles. Sunlight strikes the hemisphere tilted towards the
Sun at a higher angle than the hemisphere tilted away from the Sun.

17. When are the solstices?
• Solstice-- when the Sun reaches its greatest distance north or south of
the equator
• The summer solstice occurs on June 21 or 22. (longest period of
daylight of the year)
• The winter solstice occurs on December 21 or 22. (shortest period of
daylight for the year)

18. Equinox
• An equinox occurs when the Sun is directly above the Earth’s equator.
• Daylight hours and night time hours is nearly equal all over the world.
• Neither the northern hemisphere nor the southern hemisphere is tilted
toward the Sun.
• Spring equinox—March 20 or 21
• Fall equinox –September 22 or 23