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The True “Size Scales” & Structures in the Universe!  (…BUT, what did the Ancients know…? ) Link to Video, “Star Size Comparison”,

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Presentation on theme: "The True “Size Scales” & Structures in the Universe!  (…BUT, what did the Ancients know…? ) Link to Video, “Star Size Comparison”,"— Presentation transcript:

1 The True “Size Scales” & Structures in the Universe!  (…BUT, what did the Ancients know…? ) Link to Video, “Star Size Comparison”, eh1BH34Q

2 Medieval artistic representation of a spherical Earth, with compartments representing earth, air, and water (c. 1400). Shape of the Earth? Looks Good! But how do we know it’s NOT “Flat”? 

3 When a ship is at the horizon, its lower part is invisible due to Earth's curvature. This was one of the first arguments favoring a round-Earth model. Round Earth  Can’t see over the “Horizon”!

4 The only shape that would always cast a circular shadow is a sphere. Shape of the Earth: Greek Philosopher Aristotle (384 – 322 B.C.) Round Earth umbra (dark shadow) during the August 2008 lunar eclipse.

5 Aristotle noticed that people could see different stars and constellations depending on how far north or south they were, which also suggested that the Earth was spherical. Q: Why can’t we see ALL the Constellations? (..why “Northern” vs. “Southern” ones?)

6 In Summary, Earth is (roughly) Spherical:

7 Size of the Earth: Eratosthenes of Cyrene (276 – 194 B.C.) Correct (Modern) Value: 40,007.9 km!

8 Size of the Moon (relative to Earth): Aristarchus of Samos (310 – 230 B.C.) (Actually, Eclipse timing was used):  R Luna ~ ¼ R Earth ~ 1,740 km!

9 (…of course, Nobody’s Perfect…):

10 Distance to the Moon (with Earth’s & Luna’s sizes known):  D Luna ~ 50 x R Earth ~ 380,000 km (~ 238,000 Miles)!

11 D Luna ~ 50 x R Earth ~ 380,000 km (~ 238,000 Miles) : Visualizing this Earth  Moon Distance, to scale... (But of course, the Luna’s true orbit about Earth is NOT Perfectly Circular, but is Elliptical…) :

12 Distance to the Sun: Aristarchus of Samos …so, who remembers their Trigonometry…?!  D Sun ~ 400 x D Luna ~ 150,000,000 km (~ 93 Million Miles)!

13 Aristarchus's 3rd century BCE calculations on the relative sizes of (from left) the Sun, Earth and Moon, from a 10th century AD Greek copy. Size of the Sun: Aristarchus of Samos (again!)  Sun & Moon look same size (coincidence!) + Sun ~400 x farther…

14 Putting the Sun’s size in Perspective... R Sun ~ 700,000 km ~ 400 x R Luna ~ 100 x R Earth ~ 2 x Earth-Moon Distance! (Earth & Luna would fit within the Sun 4 times back-to-back!)  The Ancient Philosophers – except Aristarchus! – believed that the Sun orbited the Earth…  Q: Does this make sense…?


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