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
The True“Size Scales”
& Structures in the
Link to Video,
“Star Size Comparison”,
(…BUT, what did the
Ancients know…? )
Shape of the Earth?
Medieval artistic representation
of a spherical Earth, with
earth, air, and water (c. 1400).
But how do we know it’s NOT “Flat”?
Round Earth Can’t see over the “Horizon”!
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.
Shape of the Earth: Greek Philosopher Aristotle (384 – 322 B.C.)
Round Earth umbra
(dark shadow) during
the August 2008
The only shape that would always cast a circular shadow is a sphere.
Q: Why can’t we see ALL the Constellations?
(..why “Northern” vs. “Southern” ones?)
Aristotlenoticed 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.
In Summary, Earth is (roughly) Spherical:
Size of the Earth: Eratosthenes of Cyrene (276 – 194 B.C.)
Correct (Modern) Value: 40,007.9 km!
Size of the Moon (relative to Earth): Aristarchus of Samos
(310 – 230 B.C.)
(Actually, Eclipse timing
RLuna ~ ¼ REarth~ 3,500 km!
(…of course, Nobody’s Perfect…):
Distance to the Moon (with Earth’s & Luna’s sizes known):
DLuna ~ 50 x REarth~ 380,000 km (~ 238,000 Miles)!
Visualizing this Earth Moon Distance, to scale . . .
DLuna ~ 50 x REarth~ 380,000 km (~ 238,000 Miles) :
(But of course, the Luna’s true orbit about Earth
is NOT Perfectly Circular, but is Elliptical…) :
Distance to the Sun: Aristarchus of Samos
…so, who remembers their Trigonometry…?!
DSun ~ 400 x DLuna~ 150,000,000 km (~ 93 Million Miles)!
Size of the Sun: Aristarchus of Samos (again!)
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.
Sun & Moon look same size (coincidence!) + Sun ~400 x farther…
Sun BIGGER than Luna…
Putting the Sun’s sizein Perspective. . .
RSun~ 700,000 km~ 400 x RLuna ~ 100 x REarth~ 2x Earth-Moon Distance!
(Earth & Luna would fit within
the Sun 4 times back-to-back!)