Lab 3

Lab 3: The Hubble Ultra Deep Field

Used with permission from "Engaging in Astronomical Inquiry," by Stephanie Slater, Timothy Slater, and Daniel Lyons. Copyright W.H. Freeman and Company, New York, 2010.

Background

It is difficult to overestimate the impact that the Hubble Deep Field (HDF) image had on astronomy in the mid-1990s. Although astronomers had undertaken observations with similar goals prior to the release of the HDF, when it was new, it provided a wealth of data on galaxies that allowed astronomers to address a number of unsolved questions about the galaxies in the Universe. The later Hubble Space Telescope image known as the “Hubble Ultra Deep Field” reveals a variety of previously unknown objects in the very distant universe that can be systematically and scientifically counted, organized, and classified.

Phase I: Exploration

1) Access the online Hubble Ultra Deep Field Image. You might be able to make it larger and smaller by “left clicking” on the image with your mouse. Most of these objects are galaxies far, far from Earth. However, a few objects are nearby stars, as indicated by “four points” on the image, as displayed in the image below.
How many stars can you find?      

2) Again, most of the objects in the Hubble Ultra Deep Field image are not individual stars, but actually distant galaxies—isolated collections of millions or billions of stars that look like a tiny dot or cloud. Determine how many galaxies are found in the image. Since counting each galaxy is not practical, one strategy for estimating the total number is to precisely count the number of galaxies in one small section of the image, then multiply the result by the appropriate number so that we have an estimate for the number of galaxies in the whole image. For example, if we counted the number of galaxies in 1/4 of the image, then we would multiply the result by 4 to find the approximate number of galaxies in the entire image (note that even this is impractical, as 1/4 of the image still contains too many galaxies to count one by one). Keep in mind, every point of light that is not a star that you identified above is indeed a galaxy... even the smallest dots!

What is the total number of galaxies in this image?      

3) a. Some of the galaxies are orange-red in color, while others are white and still others are blue. What is the most common color of galaxy in the image?  b. Precisely explain how you determined this, not just “I looked and saw more of this color.”  A precise explanation should enable someone to repeat your process and (hopefully) obtain the same results.

4) a. If we assume that all of the galaxies in this image have the same diameter, then the ones that are close appear larger and the ones that are more distant appear smaller. Are most of the galaxies in this image relatively near or relatively far? b. What is your evidence?

Phase II: Does the Evidence Match a Given Conclusion

5) Access the interactive Ultra Hubble Deep Field site through the SkyWalker website.

The green circle in the top left hand corner is a sort of “magnifying glass” that you can drag around that will let you look at close up portions of the Hubble Ultra Deep Field. Note that the picture is about 8 green circles wide and 10 green circles tall, for a total of about 80 green circles over the whole image.

Make rough sketches of the five closest galaxies you can find in the image, concentrating on the galaxy itself and not any background galaxies in the circle.

6)  a.  Consider the research question,"What is the most common type of nearby galaxy?" If a fellow student proposed a generalization that "nearby galaxies are equally split between round, featureless galaxies and elongated, spiral shaped galaxies," would you agree or disagree with this generalization based on the evidence you collected above on the shapes of nearby galaxies? This is not your opinion.  It can be read as: "Would you draw the same conclusion?"  b.  State specific evidence you will use.  c.  Explain your reasoning which should cite the evidence previously stated.  

Phase III: What conclusions can you draw from this evidence?

The Hubble Ultra Deep Field is one of the most important images in astronomy because it shows some of the most distant galaxies in the universe. What conclusions and generalizations can you make from the following data collected by a student by randomly positioning the green circle in an effort to answer the question, "What is the general distribution of galaxy colors?" Explain your reasoning and provide the specific evidence you are using, with sketches or pie charts or graphs if necessary, to support your reasoning.

Green Circle Sample Number	Number of Red-Orange Galaxies	Number of Blue-White Galaxies
1	7	27
2	10	16
3	15	19
4	10	29
5	12	27

Data collected at UDF SkyWalker V1.0

Phase IV:  What evidence do you need to pursue?

Imagine your team has been assigned the task of writing a news brief for your favorite news blog about the differences between the numbers of nearby and extremely distant galaxies in the universe. Describe precisely what evidence you would need to collect, and how you would do it, in order to answer the research question of, “Are there more nearby galaxies or more extremely distant galaxies?” You do not need to actually complete the steps in the procedure you are writing.

8) Create a detailed, step-by-step description of evidence that needs to be collected and a complete explanation of how this could be done—not just “move the green circle around and look at how many big and how many small,” but exactly what would someone need to do, step- by-step, to accomplish this. You might include a table and sketches—the goal is to be precise and detailed enough that someone else could follow your procedure.

Phase V: Formulate a question, pursue evidence, and justify your conclusion

Your task is to design an answerable research question, propose a plan to pursue evidence, collect data using the interactive Ultra Hubble Deep Field site (or another suitable source pre- approved by your lab instructor), and create an evidence-based conclusion about the characteristics of galaxies in our universe that we have not previously addressed.

Specific Research Question:

Step-by-Step Procedure to Collect Evidence:

Data Table and/or Results:

Evidence-based Conclusion Statement:

Phase VI: Summary

Create a 50-word summary, in your own words, that describes the characteristics and distribution of galaxies in our universe. You should cite specific evidence that you have collected in your description, not describe what you have learned in class or elsewhere. Feel free to create and label sketches to illustrate your response.