1. Scales of Size and Time
Astronomy deals with objects on a vast range of size scales and time scales.
Most of these size and time scales are way beyond our every-day experience.
Humans, the Earth, and even the solar system are tiny and unimportant on cosmic scales.

2. A Campus Scene
16 x 16 m

3. A City View
1 mile x 1 mile

4. The Landscape of Pennsylvania
100 miles x 100 miles

5. Diameter of the Earth: 12,756 km

6. Distance Earth – Moon: 384,000 km
Earth and Moon
Distance Earth – Moon: 384,000 km

7. Earth Orbiting Around the Sun
Distance Sun – Earth = 150,000,000 km

8. Earth Orbiting Around the Sun-AU
In order to avoid large numbers beyond our imagination, we introduce new units:
1 Astronomical Unit (AU) = Distance Sun – Earth = 150 million km

9. The Solar System
Approx. 100 AU

10. (Almost) Empty Space Around Our Solar System
Approx. 10,000 AU

11. The Solar Neighborhood
Approx. 17 light years

12. The Solar Neighborhood (2)
New distance scale:
1 light year (ly) =
Distance traveled by light in 1 year
= 63,000 AU = 1013 km
= 10,000,000,000,000 km
(= zeros)
= 10 trillion km
Approx. 17 light years
Nearest star to the Sun:
Proxima Centauri, at a distance of 4.2 light years

13. The Extended Solar Neighborhood
Approx. 1,700 light years

14. Diameter of the Milky Way: ~ 75,000 ly
The Milky Way Galaxy
Diameter of the Milky Way: ~ 75,000 ly

15. The Local Group of Galaxies
Distance to the nearest large galaxies: several million light years

16. The Universe on Very Large Scales
Clusters of galaxies are grouped into superclusters.
Superclusters form filaments and walls around voids.

17. A Campus Scene
16 x 16 m

18. A Student Asleep
1 x 1 m

19. The Back of a Hand
10-1 x m

20. Skin
10-2 x m

21. Skin
10-3 x m
millimeter

22. Skin
10-4 x m

23. A Capillary Vessel
10-5 x m

24. A Ruffly Lymphocyte
10-6 x m
micron

25. Coils of DNA
10-7 x m

26. Coils of DNA
10-8 x m

27. The Genetic Message
10-9 x m
nanometer

28. A Sense of Time
If we were to compress the time since the Big Bang into one year, and make the time of the Big Bang January 1,
The Earth was formed in mid-September.
The mammals appeared on December 26.
All human prehistory (from the first known stone tools) and history have occurred in the last 1/2 hour of New Year's Eve.
Thus, all of human history is but a fleeting instant on the cosmic timescale.