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

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Presentation on theme: "Scales in Space and Time in the Cosmos By Dr. Harold Williams of Montgomery College Planetarium"— Presentation transcript:

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

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 Image courtesy of The Cosmic Perspective by Bennett, Donahue, Schneider, & Voit; Addison Wesley, 2002

4 16 x 16 m A Campus Scene

5 1 mile x 1 mile A City View

6 100 miles x 100 miles The Landscape of Pennsylvania

7 Diameter of the Earth: 12,756 km Earth

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

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

10 Approx. 100 AU The Solar System

11 The speed of light: c = 3x10 5 km/s. Source Distance (km) Light Travel time London 6,000 0.02 s Moon 385,000 1.3 s Sun1.5 x 10 8 500 s (8.3 min) Jupiter7.8 x 10 8 43 min Nearest Star4 x 10 13 4.3 years Most Distant Galaxy1.4 x 10 23 14 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 Approx. 10,000 AU (Almost) Empty Space Around our Solar System

15 Approx. 17 light years The Solar Neighborhood

16 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

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






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


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


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


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

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 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!

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 Until ~ 6 billion years ago, gravity of matter was stronger than acceleration Today, acceleration due to dark energy dominates.

42 Scientific Notation Video ?video_id=119236 ?video_id=119236

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