Keep Looking Up

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# Keep Looking Up - PowerPoint PPT Presentation

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).

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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
The celestial sphere appears to rotate about the celestial poles (completing one cycle in one day).
Celestial north pole stays still (North star aka Polaris)
• Stars appear to move in counterclockwise fashion.
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.
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.
The Moon moves west to east relative to the stars (completing one cycle in one month).
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.
Wanderers
• Only 5 planets to the naked eye.
• Mercury, Venus, Mars, Jupiter, Saturn