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Keep Looking Up Topic 2 Part 1

Keep Looking Up

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Keep Looking Up. Topic 2 Part 1. ``Astronomy compels the soul to look upward and leads us from this world to another.'' - Plato. Early Astronomy. Early Models. Big Dipper. Orion. Scorpio. The celestial sphere appears to rotate about the celestial poles (completing one cycle in one day). - PowerPoint PPT Presentation

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Page 1: Keep Looking Up

Keep Looking Up

Topic 2 Part 1

Page 2: Keep Looking Up

``Astronomy compels the soul to look upward and leads us from this world to another.'' - Plato

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Early Astronomy

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Early Models

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Big Dipper

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Orion

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Scorpio

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Winter sky

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The celestial sphere appears to rotate about the celestial poles (completing

one cycle in one day).

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• Celestial north pole stays still (North star aka Polaris)

• Stars appear to move in counterclockwise fashion.

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Question: What causes the observed circular motions of the stars, Sun, Moon,

and planets about the celestial pole?

• Hypothesis 1: The Earth is stationary, and the stars, Sun, Moon, and planets revolve around it.

• Hypothesis 2: The stars, Sun, Moon, and planets are not revolving about the Earth; it is the Earth which is rotating about its polar axis, once per day.

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This or that?

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The Sun moves west to east relative to the stars (completing one cycle in one

year).

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Question: What causes this apparent motion of the Sun relative to the background stars?

• Hypothesis 1: The Earth is stationary, and the Sun revolves around it at a slightly slower rate than the celestial sphere does.

• Hypothesis 2: The Earth revolves around the Sun, once per year.

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This or that?

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The Moon moves west to east relative to the stars (completing one cycle in one month).

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Question: What causes this apparent motion of the Moon relative to the background stars?

• Hypothesis 1: The Earth is stationary at the center of the universe, and the Moon revolves around it a a slower rate than the celestial sphere does.

• Hypothesis 2: The Moon revolves around the rotating Earth, once per month.

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The planets sometimes move west to east, sometimes east to west, relative to

the stars.

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Wanderers

• Only 5 planets to the naked eye.

• Mercury, Venus, Mars, Jupiter, Saturn

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This or that?