De-Coding Starlight: From Pixels to Images - High School

Materials

1. Student Handout Sheet
2. Calculator
3. Colored Pencils (with at least five different colors for each student group)

Objectives

1. The student will use data collected from the Chandra X-ray Observatory to calculate the average pixel intensity of X-ray emissions from a supernova remnant. (A pixel is any of the small discrete grid squares that together constitute an image).

2. The student will order average pixel intensity levels into range levels and associate image colors to each level to create an image of a supernova remnant.

3. The student will interpret a "false color" image formed from real data and develop explanations as to why scientists employ computers to process and analyze astronomical data.

Preparation

1. Before conducting this activity, the students should be introduced to and understand the mission and operation of the Chandra X-ray Observatory. Significant introductory resources are available at the Chandra web site (http://chandra.harvard.edu). Specifically, the following areas of the web site concern the objectives of this activity.

   1. The Chandra Mission http://chandra.harvard.edu/about/axaf_mission.html

   2. Data Collection Instruments on Chandra http://chandra.harvard.edu/about/science_instruments.html

   3. Chandra Images and False Color http://chandra.harvard.edu/photo/false_color.html

2. In the activity, the students will develop an image for the supernova remnant Cassiopeia A (Cas A). Prior to conducting the activity, the students should be exposed to the basic components of supernova remnants. There are several images of supernova remnants, including Cas A, at the Chandra web site (http://chandra.harvard.edu/photo/category/snr.html). Also, below is an image and feature discussion of Cas A that the instructor should review before conducting the activity.

3. One of the most challenging parts of the activity for the students is assigning colors to intensity ranges (Task B, steps 2 and 3 - see the student handout sheet). This process is called "binning" and commonly occurs in image processing. Binning is extremely important to see image features. In the activity, students choose their own colors and intensity ranges and are instructed to have the teacher check their binning before coloring the image. To make these steps easier, the instructor may wish to have pre-assigned colors and intensity ranges instead of having the students do this.

4. One of the main purposes of this activity is to show how numerical data from Chandra is converted to images of astronomical objects. A "Chandra Chronicles" article, titled "A River of Data Flows Through the CIAO Waterworks (http://chandra.harvard.edu/chronicle/0401/ciao_data.html)," discusses how computers assist Chandra scientists in converting numerical data to graphical images. The article includes pictures of the data received from Chandra, as well as a discussion of the software used to convert the data into images. Before conducting the activity, the teacher may find this background information helpful when explaining the activity to the students. The teacher may also want the students to read this information before starting the activity.

5. Some of the data are intentionally missing. Again, this is a realistic challenge confronted by scientists. Depending on student ability you may use a variety of techniques ranging from estimation to statistical techniques to handle these data omissions.