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