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The Moon. Topics:. Why do we only see one face of the Moon? Why do we see phases of the Moon? What causes eclipses?. Phases of Moon. Half of the Moon is illuminated by the Sun and half is dark. We see a changing combination of the bright and dark faces as the Moon orbits Earth.

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Presentation Transcript
The moon l.jpg
The Moon

Topics:

  • Why do we only see one face of the Moon?

  • Why do we see phases of the Moon?

  • What causes eclipses?


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Phases of Moon

  • Half of the Moon is illuminated by the Sun and half is dark.

  • We see a changing combination of the bright and dark faces as the Moon orbits Earth.

How to Simulate Lunar Phases


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Phases of the Moon

Phases of the Moon


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Phases of the Moon: 29.5-day cycle

new

crescent

first quarter

gibbous

full

gibbous

last quarter

crescent

}

  • waxing

  • Moon visible in afternoon/evening

  • Gets “fuller” and rises later each day

}

  • waning

  • Moon visible in late night/morning

  • Gets “less” and sets later each day


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Moon Rise/Set by Phase

Time the Moon Rises and Sets for Different Phases


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Thought Question

It’s 9 A.M. You look up in the sky and see a moon with half its face bright and half dark. What phase is it?

  • First quarter

  • Waxing gibbous

  • Third quarter

  • Half moon


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Thought Question

It’s 9 A.M.You look up in the sky and see a moon with half its face bright and half dark. What phase is it?

  • First quarter

  • Waxing gibbous

  • Third quarter

  • Half moon



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What causes eclipses? - Shadows

  • The Sun is the source of visible light in the solar system

  • The Earth and Moon cast shadows.

  • When either passes through the other’s shadow, we have an eclipse.


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When can eclipses occur?

  • Lunar eclipses can occur only at full moon.

  • Lunar eclipses can be penumbral, partial, or total.


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Solar Eclipse

Evolution of a Total Solar Eclipse


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When can eclipses occur?

  • Solar eclipses can occur only at new moon.

  • Solar eclipses can be partial, total, or annular.





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Why don’t we have an eclipse at every new and full moon?

  • The Moon’s orbit is tilted 5° to ecliptic plane.

  • So we have about two eclipse seasons each year, with a lunar eclipse at new moon and solar eclipse at full moon.


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Eclipses - Shadows

  • Lunar Eclipse

    • Moon passing through Earth’s shadow

    • Full moon

    • Three types:

      • Total - through umbra

      • Partial - partially through umbra

      • Penumbral - through penumbra

  • Solar Eclipse

    • Moon’s shadow crosses the Earth

    • New moon

    • Three types:

      • Total - umbra

      • Partial - penumbra (outside misses earth)

      • Annular - Moon farther from Earth, umbra doesn’t reach Earth


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Planets Known in Ancient Times

  • Mercury

    • difficult to see; always close to Sun in sky

  • Venus

    • very bright when visible; morning or evening “star”

  • Mars

    • noticeably red

  • Jupiter

    • very bright

  • Saturn

    • moderately bright


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Sun

Norse Sol

Sunday

Mars

Norse Tyr

Tuesday

Venus

Norse

Frigga

Friday

Mercury

Germanic

Woden

Wednesday

Jupiter

Norse Thor

Thursday

Moon

Germanic

Mani

Monday

Saturn

Roman

Saturday

Type in “week” in Wikipedia…and also

“days of the week”.

Why are there 7 days in a week?

The ancient Babylonians are known to have observed a seven-day week; each day dedicated to a different deity. The significance of seven comes from Babylonian astronomy. There are the seven heavenly bodies or luminaries normally visible to the naked eye (the Sun, Moon, and 5 visible planets), and they associated each with a deity. The word planet means “wanderer” in Greek.


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What was once so mysterious about the movement of planets in our sky?

  • Planets usually move slightly eastwardfrom night to night relative to the stars.

  • But, sometimes they go westward relative to the stars for a few weeks: apparent retrograde motion.



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Explaining Apparent Retrograde Motion in its orbit.

  • Easy for us to explain: this occurs when we “lap” another planet (or when Mercury or Venus laps us).

  • But it is very difficult to explain if you think that Earth is the center of the universe!

  • If the Earth is moving, why don’t we see parallax in the positions of the stars?