Chapter 19, Section 2Phases, Eclipses, and

TidesFriday, April 30, 2010

Pages 646 -- 654

ObjectivesDescribe the causes of the moon’s phases.

Explain what causes solar and lunar eclipses.

Identify the cause of the tides.

Vocabulary WordsPhaseEclipseSolar eclipseUmbraPenumbraLunar eclipseTide Gravity

Phases, Eclipses, and Tides

The positions of the moon, Earth, and the sun cause the phases of the moon, eclipses, and tides.

The moon rotates on its own axis.It takes 27.3 days to revolve around Earth.

The orbit is oval shape.

Moon Phases The different shape of the moon as seen from Earth are called phases.

The moon will go through its entire set of phases each time it revolves around Earth (once a month).

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Moon Phases -- cont’d

Moon phases are caused by the relative positions of the moon, Earth, and the sun.

The phase of the moon also depends on how much sunlight shines on the side of the moon that faces Earth.

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Cycle of the Phases

Each cycle is approximately 29.5 days. About 29.5 days after the last new moon, a new moon will appear again.

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Eclipses An eclipse occurs when the moon’s shadow hits Earth or Earth’s shadow hits the moon.

There are two types of eclipses: Solar (sun) Lunar (moon)

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Solar Eclipses Solar eclipses occur when the moon passes between Earth and the sun.

The sunlight is blocked from reaching Earth.

A solar eclipse is really just a new moon blocking our view of the sun.

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Total Solar Eclipse

A total solar eclipse occurs when the umbra (the darkest part of the moon’s shadow) completely blocks the sun.

The sky is so dark that stars are visible.

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Partial Solar Eclipse

The penumbra is a shadow that is not as dark as the umbra.

Because the penumbra is larger and not as dark, part of the sun is visible from Earth.

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Lunar Eclipses A lunar eclipse occurs at a full moon when Earth is directly between the moon and the sun.

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Total Lunar Eclipse

When the moon is in Earth’s umbra (darkest part of the shadow), you will see a total lunar eclipse.

A total lunar eclipse can be seen anywhere where the moon is visible.

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Partial Lunar Eclipse

In a partial lunar eclipse, the moon passes partly into the umbra of Earth’s shadow.

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TidesTides occur mainly because of the differences in how much the moon pulls on different parts of the Earth.

The pull is called gravitational pull.

The force of the pull depends on the masses of the objects and the distance between them.

Tides -- cont’d As Earth rotates, the moon’s gravity pulls water toward the point on Earth’s surface closest to the moon (high tide).

A second high tide occurs on the opposite side of Earth.

Low tides occur about halfway between the two high tides.

Tides occur in a 25-hour cycle. The shape of bays, inlets, and ocean floor also affect the flow of water, the height of the water, and the timing of the tides.

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Hopewell Rocks in New Brunswick, Canadaduring low tide -- people are walking along thebeach!

Hopewell Rocks during high tide -- where’s the beach?

ReviewWhy does the moon change its phase as the month progresses?

Describe the relative positions of Earth, the sun, and the moon during a solar eclipse.

Describe the relative positions of Earth, the sun, and the moon during a lunar eclipse.

Why are a “day” and a “year” on the moon the same length?

HomeworkWorkbook 19.2 (5/5)Vocabulary quiz 19.2 (5/5)