1. Scales in Space and Time in the Cosmos
By Dr. Harold Williams
of Montgomery College Planetarium
Title slide

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. Size and Scale of the Universe
Realms of the Universe
Image courtesy of The Cosmic Perspective by Bennett, Donahue, Schneider, & Voit; Addison Wesley, 2002

4. A Campus Scene
16 x 16 m

5. A City View
1 mile x 1 mile

6. The Landscape of Pennsylvania
100 miles x 100 miles

7. Diameter of the Earth: 12,756 km

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

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

10. The Solar System
Approx. 100 AU

11. The speed of light: c = 3x105 km/s.
Source Distance (km) Light Travel time
London 6, s
Moon , s
Sun x s (8.3 min)
Jupiter x min
Nearest Star 4 x years
Most Distant Galaxy 1.4 x billion years
Whenever you see "light-(time)", that means we are talking about distance, not time.
1 light year = 10 trillion km

12. Survey Question
Sound travels at a speed of 300 meters per second. In analogy to the light-year, what does 1 sound-minute equal?
The time sound takes to travel 300 meters.
The time delay of a sound heard 300 meters away.
The distance traveled by sound in 1 minute.
The speed of sound 1 minute later.

13. Survey Question
If the Universe is infinite in size and 14 billion years old, the most distant object that we could ever hope to see is:
1) 100,000 light-years away
2) 14 billion light-years away
3) 14 billion years away
4) there is no limit – if we look hard enough, we will see all objects.

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

15. The Solar Neighborhood
Approx. 17 light years

16. The Solar Neighborhood
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
Nearest star to the Sun:
Proxima Centauri, at a distance of 4.2 light years
Approx. 17 light years

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

20. To get another sense of this…
If Earth were a golf ball, the sun would be 15 meters wide.
You would be able to fit 960,000 Earths (almost a million) in the Sun…
With 1 million golf balls, you would be able to fill an entire school bus with nothing but golf balls!

22. Betelguese is 2x the Earth’s orbit around the Sun!
If Earth were a golf ball, Betelguese would be the size of 6 Empire State buildings stacked one on top of the other…
You could fit 262 trillion Earth’s in Betelgeuse…
If you had that many golf balls, you would fill the super bowl dome with golf balls.

23. How big is a million, billion, trillion, etc. anyway?
1 million seconds ago = 12 days ago
1 billion seconds ago = 31 years ago
1 trillion seconds ago = 31,688 years ago

24. Mu Cephei…
If Earth were a golf ball…. Mu Cephei would be the size of two Golden Gate Bridges!
You could fit 2.7 quadrillion Earth’s..
Canis Majoris
If earth were a golf ball… Canis Majoris would be the height of Mount Everest!!
You could fit 7 quadrillion Earths….
That is enough golf balls to cover the entire state of Texas with golf balls… 22 inches deep.

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

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

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

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

31. 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.

32. 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:

33. 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 …

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

35. 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 ½ hour of New Year's Eve.
All of human history is but a fleeting instant on the cosmic timescale.

36. Optical Sky

37. Near-infrared sky
Boldt et al.

38. Radio Sky

39. Soft X-ray Sky

40. Gamma-ray all-sky map
Fermi Gamma-ray Space Telescope

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

42. Scientific Notation Video