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

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”?

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”!

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.

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?)

In Summary, Earth is (roughly) Spherical:

Size of the Earth: Eratosthenes of Cyrene (276 – 194 B.C.)

=

= 50

Correct (Modern) Value: 40,007.9 km!

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!

(…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)!

( 𝟎 .𝟓 °)

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…) :

Distance to the Sun: Aristarchus of Samos

…so, who remembers their Trigonometry…?!

DSun ~ 400 x DLuna ~ 150,000,000 km (~ 93 Million Miles)!

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!)

!

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…?