Multiwavelength Astronomy: Galaxies in a Different Light Teacher Edition grades 9-12




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Multiwavelength Astronomy: Galaxies in a Different Light

Teacher Edition grades 9-12
Introduction:

Throughout this activity students should begin to realize that there is a wealth of information that we can learn about various objects even if we can't see it with our own eyes. Observing galaxies at different wavelengths enables astronomers to learn about different parts of those galaxies. Visually inspecting the multiwavelength images should enable students to recognize, for instance, that while some galaxies have features that are obscured by dust in visible light, the infrared images show the light the dust emits and what may be hidden inside of it. X-ray and radio observations give astronomers a means of seeing large-scale structure that may not be visible in ultraviolet, visible, or infrared.

An important thing to point out to your students is that the images of each galaxy are all of the same orientation and scale, as you may see in these examples that can be inspected via the Answer Guide:


  • Orientation: the x-ray image of M82 really is showing matter at right angles to the plane of the galaxy seen in the other images.

  • Scale: M100 in the ultraviolet images looks as though it could be a zoom-in of the center of the galaxy, but it is not. The crescent shape doesn't seem to strictly match the spiral arms, and yet the size and orientation of this image is the same as the others.


Prerequisites:

Prior to this activity, students should have an understanding of the electromagnetic spectrum, i.e. that radio, ultraviolet, x-rays, etc. are all forms of light with different wavelengths/energies, and because they are light, they all travel equally fast at the speed of light.

Recommendation: Have students do the NASA Ceres Project galaxy classification activity prior to this activity if they are not already aware of galaxy types. Website: http://btc.montana.edu/ceres/html/Galaxy/gal1.html
Estimated time for activity: 50 minutes
Student Product:

Students will match galaxy images taken in different wavelength regions and fill out the Student Worksheet in pairs, which includes providing justification behind their reasoning, including the coloring activity of a galaxy in two different wavelengths. After the activity, students should understand there is important information gained by observing galaxies (or anything) in different wavelengths and what galaxy features emit in those wavelengths.


Materials:

  • multiwavelength.zip file

  • computer for classroom with internet browser (no connection necessary once file is downloaded)

  • projector connected to computer

  • Standard Image Set, one for each pair of students

  • Extended Image Set, one for each pair of students

  • Student worksheets "Multiwavelength Astronomy: Your World in a Different Light", one 7 page worksheet for each pair of students

  • Student activity sheet “Multiwavelength Astronomy: False Color Galaxies”, one 2 page worksheet for each pair of students

  • Markers (blue, green, yellow, pink/orange) 1 set for each pair of students


Standards:

NSES:


  • Science as Inquiry: abilities necessary to do scientific inquiry; understanding about scientific inquiry.

  • Physical Science: motions and forces; interaction of energy and matter.

  • Earth and Space Systems: origin and evolution of the universe.

  • Science and Technology: understanding about science and technology.

  • History and Nature of Science: nature of scientific knowledge.

TEKS:


  • Scientific inquiry

  • Critical thinking and problem solving

  • Characteristics and behavior of waves

  • Force and motion

  • Properties of matter

  • Conservation of energy and momentum

  • Use of mathematical models and computer simulations to study the universe

  • Characteristics and life cycle of stars

  • Characteristics of galaxies

  • Evolution of the universe


Teacher Preparation:

Teacher must print and cut out the galaxy images from the Standard and Extended Image Sets. Recommend: print on card stock; print with low toner to enable students to see details – printing with normal toner levels makes contrast on the cards too extreme.



  • Standard Image Set: Print enough copies for each pair of students to have one entire set. Cut the image cards apart. The images will be sorted as per the following instructions. All images have a label below them indicating the wavelength of the image. Sort the cards by wavelength so there are three subsets of images – visible, radio, and ultraviolet.

  • Extended Image Set: Teacher should also print and cut out the images, but sorting is unnecessary. Print enough copies for each group to have an entire set. Recommend: print on different color card stock than Standard Image Set.

  • Teacher must also download the Answer Guide zip file and unzip it. In the classroom, have a computer available and provide a projection system* for the class to check answers simultaneously. The Answer Guide is also used while the students fill out the Student Worksheet.



Engage:

  • Project the first slide of the Answer Guide.

Begin by asking students what different wavelengths can tell us about things in the real world. Students may answer that infrared is heat so you can tell how hot something is, or that people use x-rays to see inside the body/luggage. Give the example of a doctor trying to learn more about you because you're sick. What wavelengths do doctors use? Visible light: they look you over on the outside; infrared: they take your temperature; x-rays: they have x-rays taken to be able to see through your skin/deeper inside you. If you are very ill, they may use an MRI (radio wave), or treat a cancer with gamma rays.


  • Project the second slide of the Answer Guide.

  • Group students into pairs, then pass out one Student Worksheet "Multiwavelength Astronomy: Your World in a Different Light" to each pair.

Instruct the pairs of students to read and complete pg. 1 & 2 of the worksheet while projecting the second slide of the Answer Guide, “Infrared Dog”. Point out that the dog is actually emitting the infrared radiation, as opposed to reflecting it, as it would do for a visible light image. Answers: The hot areas of the dog are the ears, eyes, and mouth. The cold areas are the areas insulated by fur and the nose. After students have answered on their sheets, ask the class what they thought the answers were and discuss why this makes sense. Infrared senses heat, so the hot areas are the areas that open to the interior of the dog’s body, while the cold areas are insulated and far from the center of the dog, except the nose, which is kept wet and cold.

  • Project the third slide after students have answered the Infrared Dog questions.

The mystery object is a pocket solar calculator. The bright areas are the circuitry.

This image is made by reflecting radiation off the calculator. The bright areas are those that reflect the X-rays. Point out that astronomers use many wavelengths. X-rays allow astronomers to peer deep inside galaxies, infrared reveals information about dust, ultraviolet can show the locations of bright, young stars, radio waves can help us see large clouds of gas that aren't hot enough to emit visible, or even infrared light.



  • Pass out the “Multiwavelength Astronomy: False Color Galaxies” sheets. Each group should get both pages 1 and 2. Pass out markers so each pair has the 4 colors.

Have each student take a sheet and color according to the legend. Students may realize while coloring that their picture does not match their partner’s. This is intentional. After students have filled in the sheets using markers, explain that both members of each pair have an image of the same galaxy. The image on pg 1 is from the radio band, and pg 2 is in the visible. Stress that the differences are due to different details seen in different wavelengths. This is how astronomers get more information by looking in different wavelengths. Sometimes they see structures that were not observable in other wavelengths. Have students note details visible in one wavelength and not the other.
Explore:

  • Project slide four “Galaxy Features.” Talk through the slide with the students.

Explain that specific parts of a galaxy emit light in different wavelengths. When astronomers take images that are in different wavelengths, they see the features that emit light there.

For instance, ultraviolet images highlight areas of the galaxy where there are hot, young stars. For spiral galaxies, this is often in the spiral arms. In visible wavelengths, these stars appear blue. Most other stars are seen when viewed in visible light, this includes stars like our sun. The nucleus (core) of a spiral galaxy has more evolved (cooler and older) red stars. In some visible images, astronomers see dark areas caused by dust that block the light coming from behind; since the dust emits light in the infrared, astronomers can detect structures, using infrared observations, that are sometimes obscured in the visible. X-rays indicate very hot gas in and around the galaxy (false colored as yellow/orange in the slide), along with very energetic stars (green). Cool gas in the galaxy is emits radio radiation. Knowing these features match certain wavelengths, astronomers can better determine the structure of the galaxies in the images.




  • Project slide five “Multiwavelength Astronomy.”

Matching sets of image cards

  • Pass out, to each pair of students, the radio and visible card sets from the Standard Image Set.

  • Have each pair designate one of themselves as a data recorder. This student will write their data on the answer sheet.

  • Ask the pairs of students to match the image cards so each visible card has a radio mate. There should be eight image card pairs. This works best when students line up the eight images from one set across the top of their desks, then match the corresponding image cards below. Then have the data recorder write down their answers on pg. 3 of their worksheet and justify their decisions in the “Reasoning” column. Give students a time limit for matching. 6-7 minutes is suggested, no more.

  • Have students put aside the radio image set. Pass out the ultraviolet card set. Ask students to match the image cards in ultraviolet and visible, so there are eight pairs, each with a visible and ultraviolet image card. The data recorder should record answers and reasoning on pg. 4 of the student worksheet. Give students the 6-7 minute time limit for matching and recording.

  • Have students put aside the visible image set. Ask students to match the objects in ultraviolet and radio, without checking their previous answers, then record answers and reasoning on pg. 5 of their worksheet. Give 6-7 minute time limit.

  • Leaving the radio-ultraviolet matches out on the desk, have students then get out their visible image card set and match them so that for each galaxy, there are three images – one in visible, one in radio, and one in ultraviolet. Have the data recorder record their answers on pg. 6. Give students a 6-7 minute time limit.

Discuss what wavelengths were the hardest to match and why. (Students may respond radio and ultraviolet. These are the two extremes of wavelength region that they were asked to match.) Ask students if different parts of a galaxy are seen more easily in some wavelengths than others (e.g., hot stars, gas, dust).


Explain:

  • Project slide six and onward. Stop at “Assessment Challenge.”

Show the Answer Guide slides one at a time so that students can check their results and rearrange, if necessary. This should be a chance for students to assess themselves in their logic for matching, but also revise and rethink their answers. Seeing the color images should also solidify why certain image cards matched, especially when details are lost in the printing.

Below is a table of the correct results:




Galaxy Name

Ultraviolet #

Visible #

Radio #

M82

I

6

F

M101

II

4

H

M31

III

3

G

M100

IV

2

A

M81

V

9

E

M33

VI

5

D

M94

VII

1

C

SMC

VIII

13

B

If you wish to review galaxy types, here is a resource list.




TYPE

Examples

Irregular

Centaurus A, Small Magellanic Cloud, Large Magellanic Cloud, M82

Elliptical

M84, M87

Spiral

M31, M33, M65, M74, M77, M81, M94, M100, M101, M104, M106

Barred Spiral

M83, NGC 1313


Evaluate:

  • Project slide fourteen “Assessment Challenge.”

Have students examine the slide and discuss with their partner which galaxy features are emitting in each image. This will have the students consider which wavelengths the images are taken in based on the features they can notice. Students should be remembering the discussion of the “Galaxy Features” slide and applying their understanding of different wavelengths based on the matching they did. There is space to record answers at the bottom of pg. 6 of the student worksheet. There is also a hint which directs students back in their worksheet to the paragraph on pg. 3 that outlines galaxy features emitting in certain wavelengths.

The paragraph is reproduced here:



Galaxy Features: When looking at galaxies in different wavelengths, the different wavelength images tend to highlight different features of the galaxy. X-rays highlight hot gas and some very energetic stars, UV shows mostly light from young stars, visible light shows areas with old stars, infrared shows dust, and radio images show light from cool diffuse gas.
Answers:

  1. Dust (infrared)

  2. Hot gas (X-Ray)

  3. Most stars (visible)

  4. Hot, young stars (ultraviolet)

  5. Cool gas (radio)


Extend:

  • Project slide fifteen “Proceed to Extended Image Answer Guide.”

  • Pass out the Extended Image Set to each pair.

  • Have students switch duties as data recorder with their partner.

Have students match these images all at once. There are images of five galaxies. Each galaxy has a visible image then either a radio or ultraviolet image to match with it. Students should end up with five pairs of images.


  • Project slide sixteen through twenty. Stop on M83.

Have students check their answers with the Answer Guide and revise as necessary.

Below is a table of the correct results:



Galaxy Name

Ultraviolet #

Visible #

Radio #

M74

IX

9

-----

M106

XI

10

-----

Cen A

X

11

-----

M87

-----

12

I

M83

-----

13

J




  • While projecting slide twenty of M83, point out to students that this is the same galaxy they colored at the beginning. See if they notice the similarities to their colorings, and note the infrared and X-Ray images which they did not see previously.



Take a few minutes with your students to look over the bonus images where extraordinary features are detected in the different wavelengths.
Appendix:

For teachers without computer projection capabilities, the final three pages of this teacher guide have the color images needed for filling out the Student Worksheet. Teachers can print this page as a transparency for the students to view while filling out the Student Worksheet.

Students should be given a chance to view all the color images in the Answer Guide to enhance comprehension, even if the teacher cannot project them. Doing this gives the students a chance to extend their knowledge by viewing infrared and X-ray wavelengths of many of these galaxies as well. Provide the link below to students while in a computer lab, or supply it as additional material:

http://www.as.utexas.edu/~randi/Multiwavelength/ClickMe.html


  • False color images of a dog photographed in the infrared

  • Arbitrary color scheme

  • Which parts are hottest? Coolest? Can you normally tell just by looking?


Galaxy Features



X-Ray: Hot Gas

Radio: Cool Gas

Visible: Most Stars

Ultraviolet:

Young, Hot Stars

Infrared: Dust

What galaxy features are emitting light in each image?



4

1

2

Assessment Challenge




3

5



* Teachers without computer projection systems see Appendix.





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