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Chapter 11, Section 1
Notes
2 Mistaken ideas about Earth?
• Earth was center of universe• Earth was considered flat
Why did Aristotle suspect the Earth was spherical?
• He observed that the Earth cast a curved shadow on the Moon during an eclipse.
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)
Is the Earth a perfect sphere?
• No, it bulges slightly at the equator and is somewhat flattened at the poles.
What causes day and night?
• The rotation of the Earth. (spinning on its axis)
How long is a complete rotation?
• About 24 hours or 1 day
How many rotations in a year?
• About 365 rotations in a year
What generates Earth’s magnetic field?
1. Movement of material inside Earth’s core2. Earth’s rotation
What is the purpose of the magnetic field?
• Protects us from harmful solar radiation by trapping many charged particles from the Sun
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.
Do magnetic poles change? Why?
• The magnetic poles move around the rotational poles in an irregular way. This can be significant over decades.
What is the shape of the Earth’s orbit?
• Earth’s orbit is an ellipse.
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.
What causes the seasons on Earth?
• The tilt of the Earth is the reason for the seasons.
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.
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)
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