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ASTR101: Introduction to Astronomy

Unit 6: The Present Universe   In this unit, you will be introduced to the contemporary worldview, the worldview developed in the twentieth century, replacing the modern worldview.  Its essential features are the distribution of matter in the universe and the concept that the space containing this matter is not the passive void of the modern worldview but rather a dynamic structure whose expansion is driving the evolution of the universe.

Unit 6 Time Advisory
This unit should take approximately 14 hours to complete.

☐    Subunit 6.1: 2.5 hours

☐    Subunit 6.2: 1.5 hours

☐    Subunit 6.3: 1 hours

☐    Subunit 6.4: 1 hour

☐    Subunit 6.5: 4 hours

☐    Subunit 6.6: 1 hour

☐    Subunit 6.7: 1 hour

☐    Assessment: 2 hours

Unit6 Learning Outcomes
Upon successful completion of this unit, the student will be able to: - Draw and label a diagram of the Milky Way Galaxy, indicating the location of the Solar System in the diagram. - Compare and contrast dark matter and ordinary matter. - Describe and explain the method Hubble used to demonstrate the existence of galaxies other than our own. - List the hierarchical structure of the universe from stars to the largest structures in the universe. - Identify and define the physical quantities that are related by Hubble’s Law. - List the structures in the universe that obey Hubble’s Law and those that do not. - Compare and contrast the roles of observation and theoretical interpretation with regard to Hubble’s Law. - Describe how Hubble’s Law is explained by the assumption of expanding space.

6.1 The Milky Way Galaxy   - Web Media: YouTube: TED Talks: “Carter Emmart Demos a 3D Atlas of the Universe” Link: YouTube: TED Talks: “Carter Emmart Demos a 3D Atlas of the Universe” (YouTube)

 Instructions: In this lecture, Carter Emmart demonstrates the
design and scale of the universe as determined by astronomical
observations and as represented by computer models.  He emphasizes
the relationship between humans and the universe and our
responsibilities toward the universe.  

 Watching this video should take approximately 10 minutes.  

 Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.
  • Reading: The Saylor Foundation’s “Unit 6: The Present Universe” Link: The Saylor Foundation’s “Unit 6: The Present Universe” (PDF)

    Instructions: This article provides an overview of the material we will cover in Unit 6.  Read it carefully, but please don’t think that you have to fix every single fact into your memory.  What you should strive for is to be sure that it makes sense to you as you are reading it and that when you are finished you can briefly summarize the main points of the reading.  You should read this both as you start and after you have finished working your way through the unit.

    Reading this article should take approximately 45 minutes.

  • Reading: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “The Nature of the Galaxy” Link: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “The Nature of the Galaxy” (HTML)

    Instructions: This article provides images of the Milky Way Galaxy in visible and in infrared light.

    Reading this article should take approximately 10 minutes.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

  • Reading: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “Components of the Galaxy” Link: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “Components of the Galaxy” (HTML)

    Instructions: This article discusses the disk, halo, and nucleus of our galaxy.  It also mentions the dark matter in our galaxy which we will discuss in more detail at the end of this unit.

    Reading this article should take approximately 15 minutes.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

6.2 Other Galaxies   - Reading: StarDate’s “Galaxies: Cities of Stars” Link: StarDate’s “Galaxies: Cities of Stars” (HTML)

 Instructions: This article describes the work of Edwin Hubble in
determining that galaxies other than the Milky Way exist.  

 Reading this article should take approximately 15 minutes.  

 Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.
  • Reading: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “Spiral Galaxies” Link: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “Spiral Galaxies” (HTML)

    Instructions: This article discusses the structure of spiral galaxies and some of their contents, and contains some beautiful images of galaxies.

    Reading this article should take approximately 20 minutes.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

  • Reading: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “Elliptical Galaxies” Link: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “Elliptical Galaxies” (HTML)

    Instructions: This article is very similar to the previous one but examines elliptical galaxies.

    Reading this article should take approximately 15 minutes.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

  • Reading: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “Irregular Galaxies” Link: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “Irregular Galaxies” (HTML)

    Instructions: This article is similar to the two previous ones but examines irregular galaxies.

    Reading this article should take approximately 10 minutes.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

6.3 Clusters and Superclusters of Galaxies   - Reading: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “Clusters of Galaxies” Link: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “Clusters of Galaxies” (HTML)

 Instructions: This article discusses the properties of clusters of
galaxies in general.  

 Reading this article should take approximately 10 minutes.  

 Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.
  • Reading: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “The Local Group of Galaxies” Link: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “The Local Group of Galaxies” (HTML)

    Instructions: The Milky Way is a member of a cluster of galaxies known as the Local Group.  This article describes the Local Group.

    Reading this article should take approximately 15 minutes.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

  • Reading: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “Superclusters of Galaxies” Link: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “Superclusters of Galaxies” (HTML)

    Instructions: This article moves from clusters of galaxies to clusters of clusters of galaxies – superclusters.

    Reading this article should take approximately 15 minutes.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

  • Reading: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “Soap Bubbles and Voids” Link: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “Soap Bubbles and Voids” (HTML)

    Instructions: This reading takes us to the final step in the hierarchy of structures in the universe: from stars to galaxies, from galaxies to clusters of galaxies, from clusters to superclusters, and finally to voids.  From here on out it is just more of the same.

    Reading this article should take approximately 15 minutes.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

6.4 Hubble’s Law   - Reading: Cornell University: Martha Haynes’ “Astronomy 2201: Hubble’s Law” Link: Cornell University: Martha Haynes’ “Astronomy 2201: Hubble’s Law” (HTML)

 Instructions: This article discusses Hubble’s Law, which is the
relationship between recessional velocity and distance.  Recessional
velocity mistakenly suggests the redshift in the spectra of distant
galaxies is a Doppler shift, which it is not.  We will later learn
that the redshift is caused by the expansion of space rather than
motion through space.  It also shows the observational evidence for
Hubble’s Law.  

 Reading this article should take approximately 15 minutes.  

 Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.

6.5 The Expansion of Space   6.5.1 The Expansion of Space Explains Hubble’s Law   - Reading: University of Virginia: John Hawley’s “Redshift” Link: University of Virginia: John Hawley’s “Redshift” (HTML)

 Instructions: This artocle introduces the concept of redshift and
explains the difference in redshift caused by motion (Doppler
redshift) and redshift caused by the expansion of space
(cosmological redshift).  Make sure you understand what redshift
measures.  

 Reading this article should take approximately 15 minutes.  

 Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.
  • Reading: The University of Surrey Teachers’ Astrophysics Resource: “The Expanding Universe” Link: The University of Surrey Teachers’ Astrophysics Resource: “The Expanding Universe” (HTML)

    Instructions: This article introduces the cosmological principle.  It also offers a nice explanation of the differences between cosmological and Doppler redshifts.

    Reading this article should take approximately 15 minutes.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

6.5.2 The Balloon Model of Expanding Space   - Reading: Exploratorium: Paul Doherty’s “Universal Balloon” Link: Exploratorium: Paul Doherty’s “Universal Balloon” (HTML)

 Instructions: This article uses an actual balloon to demonstrate
the balloon model for expanding space and encourages you to do so as
well.  

 Reading this article should take approximately 15 minutes.  

 Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.
  • Reading: University of California, Los Angeles: Ned Wright’s “Balloon Analogy in Cosmology” Link: University of California, Los Angeles: Ned Wright’s “Balloon Analogy in Cosmology” (HTML)

    Instructions: This article is a more detailed explanation of the balloon model than the previous one.

    Reading this article should take approximately 15 minutes.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

  • Reading: University of California, Riverside: Philip Gibbs’ “Where Is the Center of the Universe?” Link: University of California, Riverside: Philip Gibbs’ “Where Is the Center of the Universe?” (HTML)

    Instructions: This article is the most detailed of the three readings on the balloon model and clearly explains how the balloon model indicates that the universe has no center.  This is a difficult fact to visualize but an important property of the universe.  Make sure that this is clear to you, because in the next unit we will discuss the big bang model, a concept that leaves most people thinking that the center of the universe is where the big bang occurred.  This is a serious misconception.  As this article explains, there is no center to the universe.

    Reading this article should take approximately 30 minutes.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

6.5.3 Evidence for the Expansion of Space   - Reading: Bright Hub: Wendy A. M. Prosser’s “Explaining Expanding Universe Theory” Link: Bright Hub: Wendy A. M. Prosser’s “Explaining Expanding Universe Theory” (HTML)

 Instructions: This article discusses the nature of the expansion
and its relationship to the big bang theory.  It also includes a
section on the evidence for expanding space.  

 Reading this article should take approximately 15 minutes.  

 Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.

6.6 Dark Matter and Supermassive Black Holes   - Reading: YouTube: TED Talks: “Patricia Burchat Sheds Light on Dark Matter” Link: YouTube: TED Talks: “Patricia Burchat Sheds Light on Dark Matter” (YouTube)

 Instructions: This lecture discusses dark matter and the evidence
for its existence.  It also introduces the concept of dark energy
(totally different from dark matter), which is not covered in this
unit but will be very important in later units.  Think about it now
and you will be better prepared for the later material.  

 Watching this video should take approximately 20 minutes.  

 Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.
  • Reading: HubbleSite: “Black Holes: Gravity’s Relentless Pull” Link: HubbleSite: “Black Holes: Gravity’s Relentless Pull” (HTML)

    Instructions: This article discusses the supermassive black hole at the center of the Milky Way Galaxy.

    Reading this article should take approximately 10 minutes.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

  • Reading: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “Supermassive Black Holes” Link: The University of Tennessee, Knoxville’s Department of Physics and Astronomy: “Supermassive Black Holes” (HTML)

    Instructions: This article discusses supermassive black holes in other galaxies and their possible origin.

    Reading this article should take approximately 15 minutes.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

6.7 The Universe vs. the Visible Universe   - Reading: University of California, Berkeley’s The Universe Adventure: “The Visible Universe” Link: University of California, Berkeley’s The Universe Adventure: “The Visible Universe” (HTML)

 Instructions: This site very nicely discusses the distinction
between the visible universe and the universe.  You may sometimes
hear on TV someone say that early in the history of the universe, it
was the size of a pea.  What they should have said was the visible
universe was the size of a pea.  The universe probably is, and
always has been, infinitely large.  The pea analogy for the universe
is bad because it implies that the universe, like a pea, has a
center and edges, which it cannot.  The visible universe, however,
does have an edge.  We can only see out so far in all directions, so
in that sense the visible, or observable, universe does have an
edge.  Looking at it this way, you could say that we are at the
center of the visible universe.  This would equally be true of any
other observer anywhere in the universe.  Thus, the universe
actually has no specific center.  

 Exploring this site should take approximately 30 minutes.  

 Terms of Use: Please respect the copyright and terms of use
displayed on the webpage above.
  • Assessment: The Saylor Foundation’s “Unit 6 Assessment” Link: The Saylor Foundation’s “Unit 6 Assessment” (PDF)

    Instructions: When you have finished the entire unit, please complete this assessment without referring to the readings.  When you are finished with the assessment, you can check your answers against the Saylor Foundation’s “Unit 6 Assessment – Answer Key” (PDF).

    Completing this assessment should take approximately 2 hours.