the true “size scales” & structures in the universe!
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The True “Size Scales” & Structures in the Universe! . Link to Video, “ Star Size Comparison ”, http :// www.youtube.com/watch?v=HEheh1BH34Q. (… BUT , what did the Ancients know…? ). Shape of the Earth ?. Looks Good!. Medieval artistic representation - PowerPoint PPT PresentationTRANSCRIPT
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The True “Size Scales” & Structures in the
Universe!
(…BUT, what did the Ancients know…? )
Link to Video, “Star Size Comparison”,
http://www.youtube.com/watch?v=HEheh1BH34Q
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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”?
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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”!
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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) duringthe August 2008 lunar eclipse.
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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?)
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In Summary, Earth is (roughly) Spherical:
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Size of the Earth: Eratosthenes of Cyrene (276 – 194 B.C.)
=
= 50
Correct (Modern) Value: 40,007.9 km!
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Size of the Moon (relative to Earth): Aristarchus of Samos (310 – 230 B.C.)
(Actually, Eclipse timing was used):
RLuna ~ ¼ REarth ~ 1,740 km!
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(…of course, Nobody’s Perfect…):
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Distance to the Moon (with Earth’s & Luna’s sizes known):
DLuna ~ 50 x REarth ~ 380,000 km (~ 238,000 Miles)!
( 𝟎 .𝟓 °)
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DLuna ~ 50 x REarth ~ 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…) :
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Distance to the Sun: Aristarchus of Samos
…so, who remembers their Trigonometry…?!
DSun ~ 400 x DLuna ~ 150,000,000 km (~ 93 Million Miles)!
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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…
Sun BIGGER than Luna…
(Also!)
!
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Putting the Sun’s size in Perspective. . .
RSun ~ 700,000 km ~ 400 x RLuna ~ 100 x REarth~ 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…?