What new technologies are being used to map the galaxies? Is there a pattern to where galaxies are located? Why would we want to map the galaxies?

Galaxy Mapping
Why make maps of the galaxies?
David finds out how scientists make maps of the cosmos.
Segment length: 8:35


Edwin Hubble's proof that the universe is dynamic and that our Milky Way is not the lone galaxy provoked a renewal of questions and theories. Understanding the positions, distances, and distribution patterns of other galaxies not only provides mapping information; it gives perspective on what the earth's relationship is to the overall universal plan; it provides clues about the earth's origin; and it gives a type of structure to an indistinct concept.

The Doppler effect can explain the red shifts found in the light from galaxies. According to the Doppler effect, the more that light is shifted to longer wavelengths (meaning toward the red end of the spectrum), the faster the source of the light is moving away from the observer. Edwin Hubble found that the farther away the galaxy, the more its light is red-shifted. This means that the farther the galaxy, the faster it is moving away from us. In other words, the universe is expanding.

Consider the universe as a huge ball of bread dough, speckled throughout with raisins, each raisin denoting a galaxy. There is no definite boundary or edge, however. As this model universe is baking in the oven, yeast is making the dough expand. The expanding dough carries the raisins farther and farther apart from each other, but the size of each raisin does not increase. In the same way, space expands the distance between galaxies in the universe, but the galaxies themselves do not get larger.

We are on the threshold of new discoveries about the galaxies. Using the latest technology, Margaret Geller and John Huchra are able to analyze "slices" of the universe. If the ball of raisin-bread dough represents the universe, Geller and Huchra so far have mapped only four very thin slices of bread that don't even go all the way through the loaf. Their mapping illustrates a definite pattern to galaxy distribution. Galaxies appear to be positioned in a network of thin, curved walls that surround huge, nearly empty voids. How empty the voids are and how they arose, no one yet knows.

The "Great Wall" of the universe is the largest structure known to humans, yet its size, 500 million light years by 200 million light years, poses a challenge to cosmological theories. No one can explain how, if only known forms of matter and known forces were at work, such a large structure was formed in the time since the Big Bang. Newer technologies and continued research promise to introduce new insights into the universe.


What is your vision of a galaxy? Of space? Of the universe?


Big Bang a theory of the origin and evolution of the universe (This theory holds that approximately 2 x 1010 years ago, all matter in the universe was packed into a small agglomeration of extremely high density and temperature. It exploded, sending matter in all directions and giving rise to the expanding universe.)
Doppler effect a change in the frequency and wavelength of sound, light, or radio waves as perceived by an observer, caused by the relative motion of the source of the waves or the observer
galaxy a closed gravitational system of stars, their satellites, nebulae, and dust, that is spinning and traveling through space
light year the distance that light, traveling at 186,000 miles per second in a vacuum, travels in one year, or about 5.9 trillion miles
red shift a shift toward longer (redder) wavelengths in the spectrum of light from an object


Education Division
Mail Code F
Washington, DC 20546
(booklets: The Great Observatories for Space Astrophysics, NP-128; The Gamma-Ray Observatory,

Space Telescope Science Institute
3700 San Martin Dr.
Baltimore, MD 21218
(301) 338-4707
(slides, posters, videos, hands-on activities, brochures)

Astronomical Society of the Pacific
390 Ashton Ave.
San Francisco, CA 94112
(Universe in the Classroom newsletter)

Community resources:

Astronomy club
University departments of physics and astronomy

Main Activity

A New View
See for yourself what a difference a 3-D map can make.

You will observe models of constellations and galaxies from different vantage points to see how things look different when viewed from different locations.


    PART I

  1. Divide the class into teams of four.
  2. Have each team choose a favorite constellation or galaxy and make a paper map of it, using the acquired constellation maps as guides.


  1. Make a three-dimensional (3-D) model of your chosen constellation or galaxy. Start by transforming the cardboard into the unknown "dark matter" of space by painting or covering it with construction paper.
  2. Determine the location on the cardboard and size of stars needed to create a 3-D model of the chosen constellation.
  3. Use foil, tag board, string, and markers to create 3-D star models. Attach hanging stars to the cardboard by using varying lengths and thicknesses of string.
  4. Suspend the completed 3-D maps from the classroom ceiling.

Note: Your finished project will illustrate only an approximation of the placement of the stars. It would be impossible, using these materials, to make something to scale.


1. Lie on the floor and look up at your "night skies." Stand up and observe your creations from different locations in the room. Stand on a ladder and look "down" into your constellation. Which vantage point compares with the paper map? Would your conclusions change depending on your vantage point? Would you recognize the constellation from the different vantage points?

2. What types of technology still need to be invented to help us "see" more of the universe?

Do you have a manually-adjustable camera? Begin a collection of your own constellation photos. A camera shutter held open for 10 to 15 seconds will record most of the brightest stars in a constellation. An exposure of longer than 15 seconds will record the stars as streaks and trails. Why? What is happening to the earth? Point the camera both north and south and take some pictures. What will be the pattern of the trails?

Use a large balloon to represent our universe. Randomly place adhesive stars on the deflated balloon. Slowly inflate the balloon. What do you notice about the distances between the stars as the universe expands? Do the sizes of the stars change? Is there an edge to this universe? A center? Is the expansion infinite?

Find a book that describes the common constellations. Try to find them in the night sky. Consider how the patterns of stars reflect the mythological names given to them.

Demonstrate the Doppler effect by placing a battery-operated buzzer inside a hollow whiffle ball. Attach a 4- to 5-foot-long cord to the ball. Carefully swing the ball around in a circle above you head. Your classmates should be able to note an apparent change in the pitch of the buzzer. Take turns being in the center so that everyone can hear that the pitch does not change. In what part of the circle do you hear different sounds/pitches?

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