5. moon motions-student

7/25/2019 5. Moon Motions-student

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The Moon

-Around the Earth and in the Sky

Why do we see phases of the Moon?

When do we see the phases of the Moon? What causes eclipses?

Our goals for learning:


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Why do we see phases of the Moon?

Lunar phases are

a consequence of

the Moons 27.3-

day orbit aroundEarth


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Phases of Moon

Half of Moon is lit

by the Sun and

half is dark We see a different

amount of the

bright and dark

faces as Moonorbits


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Phases of the Moon: The View from Earth

new

crescent

first quarter

gibbous

full

gibbous

last quarter

crescent

waxingMoon visible in afternoon/evening.Gets fuller and rises later each day.

waningMoon visible in late night/morning.Gets less and sets later each day.

}

}

A 29.5-day cycle


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Moon Rise/Set by Phase


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Thought Question

What phase of the Moon is this?

A. First quarter

B. Waxing crescentC. Waxing gibbous

D. Third quarter


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We see only one side of Moon

Synchronous rotation:

the Moon rotates exactly

once with each orbit

That is why only one side

is visible from Earth


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Eclipses

Definition:

When light from an astronomical

body is blocked by another body

passing between it and the observer.


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Any object can eclipse another

For example there are binary stars called eclipsing

binaries, because they are detected when the orbiting

star is eclipsed.


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What causes eclipses?

The Astronomical bodies cast shadows.

When an object passes through anothers

shadow, there is an eclipse.


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Most Common Types of Eclipse

Solar Eclipse(Sun is blocked by

Moons shadow)

-occurs at New Moon

Lunar Eclipse

(Moon is blocked by

Earths shadow)

-occurs at Full Moon


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Types of Eclipse

Partial - Sun or Moon is partly covered.

Total - Sun or Moon is completely covered overand goes dark.

Annular - center of Sun is covered over, leaving

a ring of light.

Penumbral Eclipse - Moon is solely in thepenumbral shadow, only

mildly darkened.


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Eclipses Every Month?

The Moons orbit is tilted 5 to ecliptic plane. Most alignments

occur above or below the ecliptic. As a result we do notget an

eclipse every month.


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Eclipses Every Month?View from Earth


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When Do Eclipses Occur?We have about two eclipse seasonseach year, when

the Sun, Earth and Moon are in alignment and theMoon is on the plane of the ecliptic.


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When Do Eclipses Occur?

We then get a solar eclipse at new moon and a lunar

eclipse at full moon.


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Solar Eclipses


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Total Solar Eclipses

The Sun is 400 timeslarger than the Moon.

The Moon is 400 timescloser than the Sun.

Consequently, they appear to be about the same angular size.


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Solar Eclipses

Eye Protection Vital!


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Total Solar Eclipse, 1999


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Eye Safety

Sunlight can permanently burn out the

receptors in your eyes.

Retinas have no pain sensors, You won'tknow until it's too late!

Eclipses are especially dangerous, sincepeople are deliberately looking at the Sun.


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Eye Safety

Welder's Glass- excellent if expensive.

Telescopes with Sun filters -excellent, but need to

make sure it dies not get scratched.

Pin hole cameras -You do not look at the Sun (it's

cheap and works, but is not a cool-looking)

Mylar eclipse glasses - cheap but not recommended.(They scratch far too easily, high risk of line blindness)


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Total Solar Eclipse, Zambia 2001


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Start of

Eclipse


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Sunpartially

eclipsed

Second Contact: the


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Second Contact: the

Beginning of Totality


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Totality !

Z bi t T t lit


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Zambia at Totality

Cl f Ed d i T t lit


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Close-up of Edge during Totality

(Baileys Beads)


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Diamond Ring : End of Totality

Composite of Entire Eclipse


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Composite of Entire Eclipse,

Zambia 2001


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Annular Eclipses

Moon is further away, so its angular size is

slightly smaller than the Sun's angular size.


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Annular Eclipse Sequence

Greenland, 2003

Partial Eclipse at Sunset


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Partial Eclipse at Sunset,

WA, July 2000


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Partial Eclipse at Sunset sequence,

WA, July 2000


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Total Lunar Eclipse


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Lunar Eclipse

M b i i t b li d ( ti l)


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Moon beginning to be eclipsed (partial)

Moon mostl eclipsed


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Moon mostly eclipsed


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Moon eclipsed by penumbra



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End of Totality


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End of Totality

Moon still in penumbra


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Moon still in penumbra

Moon coming out of shadow


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Moon coming out of shadow


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Full Sequence of Total Lunar Eclipse

P di ti E li


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Predicting Eclipses Eclipses recur with the 18 yr, 11 1/3 day

saros cycle, but type (e.g., partial, total)and location may vary.


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What have we learned?

Why do we see phases of the Moon? Half the Moon is lit by the Sun; half is in

shadow, and its appearance to us is

determined by the relative positions of Sun,

Moon, and Earth during the Moon's orbit.

What causes eclipses?

Lunar eclipse: Earths shadow on the Moon

Solar eclipse: Moons shadow on Earth Tilt of Moons orbit means eclipses occur

during two periods each year

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