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

Background and Purpose

In an effort to learn more about black holes, pulsars, supernovas, and other high-energy astronomical events, NASA launched the Chandra X-ray Observatory in 1999. Chandra is the largest space telescope ever launched and detects "invisible" X-ray radiation, which is often the only way that scientists can pinpoint and understand high-energy events in our universe.

Computer aided data collection and processing is an essential facet of astronomical research using space- and ground-based telescopes. Every 8 hours, Chandra downloads millions of pieces of information to Earth. To control, process, and analyze this flood of numbers, scientists rely on computers, not only to do calculations, but also to change numbers into pictures. The final results of these analyses are wonderful and exciting images that expand understanding of the universe for not only scientists, but also decision-makers and the general public.

Although computers are used extensively, scientists and programmers go through painstaking calibration and validation processes to ensure that computers produce technically correct images. As Dr. Neil Comins so eloquently states*, "These images create an impression of the glamour of science in the public mind that is not entirely realistic. The process of transforming [i.e., by using computers] most telescope data into accurate and meaningful images is long, involved, unglamorous, and exacting. Make a mistake in one of dozens of parameters or steps in the analysis and you will get inaccurate results."

The process of making the computer-generated images from X-ray data collected by Chandra involves the use of "false color." X-rays cannot be seen by human eyes, and therefore, have no "color." Visual representation of X-ray data, as well as radio, infrared, ultraviolet, and gamma, involves the use of "false color" techniques, where colors in the image represent intensity, energy, temperature, or another property of the radiation. Scientists use different "false colors" to highlight different properties of the astronomical object being studied. Ultimately, it is important that anyone viewing these images understands that "false color" image processing is being used and the object would not have this appearance if viewed by the naked human eye.

The purpose of this activity is to take students "gently" through the steps of data and image processing with actual data from the Chandra X-ray Observatory. Students will develop that data shown in the image, and also, the "false colors" used to display the image. The data for this activity have undergone some pre-analysis by Chandra scientists for student manageability purposes, but the activity retains the basic principles of data analysis.

*Comins, N.F. (2001). Heavenly Errors, Columbia University Press, New York.