phases, eclipses, tides and and the moon as a clock

Phases, Eclipses, Tides and

And the moon as a clock.

Why do we only see one side of the moon?

• We see one side of the moon because it rotates and revolves at the same rate.

• Synchronous rotation

• Why is there a full moon and not an eclipse every month?

Moon Phases:

• From New Moon to Full the visible portion of the Moon increases from the right…

• From Full to New the Left side is visible

Terms:

• Waxing: Getting Bigger• Waning: Getting Smaller

• Waxing Crescent: anything between a New moon and 1st Quarter moon.

• Waxing Gibbous: anything between a 1st Quarter and a Full moon.

Monthly Lunar Phase…

We just had a full moon last Friday?

• What portion of the moon should be visible?

Eclipses

• Eclipses occur on other planets.

Io and Shadow

Copyright, NASA, via Cassini on route to Saturn in 2004

Two Types

• What are they?

Lunar Eclipse

Why is it red?

Why is it a dim red?

• The same reasons sunsets are red and the sky is blue.

Why is it a dim red?

Solar Eclipse

Solar Eclipse

• Why does the moon just about cover the sun perfectly even though it is smaller?

• Though 400 times smaller, it is 400 times closer and appears just as large.

Why are lunar eclipses visible over a greater range of places than solar

eclipses?

• The earth casts a bigger shadow than the moon.

Compare Shadow Size

• Umbra: darkest region of a shadow. Within the umbra an observer sees a total eclipse

• Penumbra: lighter region of a shadow. Observers see a partial eclipse if in the penumbra

Tides

Moon or Sun

• Which one do you think has a greater influence on our tides?

Tides:

• To understand tides we need to understand gravity.

• What two things affect the force of gravity?

The moon is roughly twice as important

• Even though the sun is bigger, the moon is a lot closer.

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Force of Gravity = Gm1m2

d2

This is the mathematical form of what Law?

Earth’s Tides

Earth

Earth’s Tides

EarthMoon

The moon attracts the water closest to it the strongest so it bulges outward.

Earth’s Tides

EarthMoon

The moon attracts the water closest to it the strongest so it bulges outward.It attracts the earth more than the water on the opposite side so it sort of hangs back.

Earth’s Tides

EarthMoon

The moon attracts the water closest to it the strongest so it bulges outward.It attracts the earth more than the water on the opposite side so it sort of hangs back.

Force of GravityWeak …………. .Medium ………….. Strong

Earth’s Tides

EarthMoon

The result is a tidal bulge with two high tides and two low tides.

High Tide

Low Tide

Low Tide

High Tide

How many tides are there a day?

• Two high tides and two low tides?

• Why? (Hint: How far apart are they)

Daily Tidal Cycle

EarthMoon

High Tide

Low Tide

Low Tide

High Tide

At Midnight it is High Tide at point A

A

Daily Tidal Cycle

EarthMoon

High Tide

Low Tide

Low Tide

High Tide

6 hours later at 6am the earth rotates you into an area of low tide.

A

Daily Tidal Cycle

EarthMoon

High Tide

Low Tide

Low Tide

High Tide

At Noon, another 6 hours later the earth rotates you again into high tide.

A

Daily Tidal Cycle

EarthMoon

High Tide

Low Tide

Low Tide

High Tide

Back to where it all started 6 hours later…

A

Two Special Tides

Spring Tide

• A High High Tide and Low Low Tide due to the combined gravitational forces of the moon and sun.

• Full moon• New Moon

Neap Tide

• The moon and sun fight and cancel each other out resulting in a smaller difference between high and low tides.

• 1st Quarter Moon• 3rd Quarter Moon

The Sun Using the Moon to Tell Time

The Sun Using the Moon to Tell Time

Earth

The Sun

Earth

Kitty

Using the Moon to Tell Time

The Sun

Earth

Using the Moon to Tell Time

What Time is it?

The Sun

Earth

Using the Moon to Tell Time

What Time is it during a New moon?

The Sun

Earth

Using the Moon to Tell Time

What Time is it?

The Sun

Earth

Using the Moon to Tell Time

What Time is it during a Full moon?

Using the Moon to Tell Time

• A full moon will rise at Sunset and each day the moon will rise one hour after that.

Concept Check

• Does the moon give off its own light?

• If the moon gave off its own light would we see phases?

• The moon reflects light from the sun and this is why phases occur. If it gave off its own light it would always be seen as full.

Concept Check

• Is the term the “Dark Side of the moon” a misnomer?

Concept Check

• Under which phase can you see more of the moon?

• Waxing Gibbous or Waning Gibbous?