The document traces key developments in human understanding of the cosmos from ancient times to the present. [1] Early Greek astronomers like Aristarchus and Eratosthenes made some of the first estimates of distances to celestial objects using observations and simple geometry. [2] Over centuries, improved observations and mathematical proofs allowed astronomers like Ibn al-Shatir and Tycho Brahe to refine estimates of distances within our solar system and to the sun. [3] In the 18th-19th centuries, astronomers like Herschel, Bessel and Hubble made breakthrough discoveries that revealed the vast scale of our Milky Way galaxy and that other galaxies exist far beyond it, establishing the modern scale of the observable universe at billions of

1. The Human Cosmos
in powers of ten
0
10 km
0

2. < 500 BC Ancient World
10 km ?
1

3. 200 BC Greek Astronomy
4.5 million km
Aristarchus - estimates relative distances and size of earth,
moon and sun from watching the shadow of the earth on the
moon during eclipse.
6 Eratosthenes - measured the size of the earth from the angle
the sun cast on a well at summer solstice (6100 km vs 6378
km).

4. 14th Century
Ibn al-Shatir
141 million km
Stronger
geometric
proofs revise
QuickTime™ and a
decompressor
are needed to see this picture. the estimates of
the distance to
the sun
8

5. Tycho Brahae
the 1572 supernova

6. Copernican system
the orbit of Saturn
1.52 x 109 miles
9

7. 1780 Herschel
estimates size of the Milky Way by counting
stars in each direction
9000 light years
16

8. 1838 - Friedrich Bessel
Measures distance to nearby stars by
Parallax

9. More accurate size of Milky
Way
91,500 light years
17

10. 1923 Edwin Hubble
“Nebulae” are other galaxies
Andromeda Galaxy
2,900,000 light years
QuickTime™ and a
decompressor
are needed to see this picture.
19 Discovery of the expansion of space

11. Hubble constant (H)
Shows Universe is Expanding
1/H 13 billion light years
23

12. Most distant Galaxies
1975 Dark Matter
13 billion light years
1995 Hubble Telescope
21-23 Deep Field Pictures

13. 2002 Acceleration of universal expansion
Dark Energy
15,000,000,000 light years
23