1. Scales in Space and Time in the Cosmos By Dr. Harold Williams of Montgomery College Planetarium http://montgomerycollege.edu/Departments/planet/

2. The Scale of the Cosmos 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 insignificant on cosmic scales.

3. 16 x 16 m A Campus Scene

4. 1 mile x 1 mile A City View

5. 100 miles x 100 miles The Landscape of Pennsylvania

6. Diameter of the Earth: 12,756 km Earth

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

8. Distance Sun – Earth = 150,000,000 km Earth orbiting around the Sun

9. Approx. 100 AU The Solar System

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

11. Approx. 17 light years The Solar Neighborhood

12. New distance scale: 1 light year (ly) = Distance traveled by light in 1 year = 63,000 AU = 10 13 km = 10,000,000,000,000 km (= 1 + 13 zeros) = 10 trillion km Nearest star to the Sun: Proxima Centauri, at a distance of 4.2 light years Approx. 17 light years

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

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

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

16. Large-Scale Structure Distribution of bright galaxies in the Virgo region indicates the Virgo cluster and presence of more distant, larger scale structure

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

18. Large-Scale Structure A large survey of distant galaxies shows the largest structures in the universe: Filaments and walls of galaxy superclusters, and voids, basically empty space.

19. Cosmology with the Cosmic Microwave Background If the universe was perfectly homogeneous on all scales at the time of reionization (z = 1000), then the CMB should be perfectly isotropic over the sky. Instead, it shows small-scale fluctuations:

20. Measuring the “Deceleration” of the Universe … By observing type Ia supernovae, astronomers can measure the Hubble relation at large distances Distance  recession speed Size scale of the universe  rate of expansion It was expected that this would measure the deceleration of the universe, but …

21. The Accelerating Universe Red Shift z Apparent Magnitude of Type Ia Supernovae Flat decelerating universe Flat accelerating universe In fact, SN Ia measurements showed that the universe is accelerating!

22. The Evolution and Ultimate Fate of the Universe Until ~ 6 billion years ago, gravity of matter was stronger than acceleration Today, acceleration due to dark energy dominates.