Colors that Humans Cannot See
Overview: Students observe images taken with filters and detectors that "see" other colors. They describe differences between the appearance of the Orion nebula when observed with detectors sensitive to different energies of light: visible and X-ray images.
Physical resources: remote control, video/digital camera, invisible light article, Chandra article, electromagnetic spectrum and telescopes poster.
Electronic resources: Orion "unfiltered" black and white image (visible light)
Introduction to colors we cannot see (photons with energies that our eyes don't detect):
- Instructor motivates the existence of other photons of higher energy, which human detectors (eyes) are not sensitive to, by recording light flashes from an infrared remote control with a digital camera or video camera. Example image: (IR-remote)
- There are other filters or detectors that allow us to "see" colors we can't with our eyes. Students read about these other kinds of "invisible light" and telescopes/detectors which can detect these photons, (invisible light telescopes)
- Students read about capability of Chandra. Elvis, Martin. "NASA's Chandra X-ray Observatory: A Revolution Through Resolution." Sky and Telescope, August 1999.
- Instructor introduces poster showing range of energy of different kinds of light and the different telescopes which can detect these ranges of photon energy.
Observations of the Orion Nebula in visible light and X-ray light:
- Instructor, in small groups, shows students how to open both visible light "unfiltered" image of Orion from Hubble (m42_combined_wcs.fits (FITS), and X-ray image of Orion nebula (OBSID 3744, Process: How to open a certain OBSID) and how to match frames and lock crosshairs to compare between the two images. (Process: Match frames, Process: Lock crosshairs)
- Students record in notebook or on board, the important differences between the two images, specifically using the words angular width/height, angular separation and flux.
- Students also to describe the properties of shape, texture (i.e. What would this feel like? fuzzy, lumpy, sharp, etc.) and relative locations.
- Focus question: Are the four stars with the highest X-ray light flux the same as the four stars with the highest visible light flux?
- Use Orion nebula overlay image (trapezium visible xray contours) to wrap up the discussion that different objects can have different fluxes when different energies of light are collected.
- If time, students can make their own overlay image of the Orion nebula, by making a 3-color image, and loading the X-ray image as green and the visible image as red. They will then see a range of colors for the objects (red through yellow through green), depending on which flux is higher.
- Students save their matched frames as a jpeg, including color bar information: From ds9, choose "File...Save image..." and then select JPEG.
- Typically any digital camera is sensitive to any infrared remote control. Test before you use with students to make sure, though.
- The important point here is to get students comfortable with using images in different energy ranges of light (parts of EM spectrum) of the same objects to begin noticing differences. In particular, the fact that stars in Orion have different fluxes in different kinds of light.
- (invisible light reflections): Example of student list of things they learned about "colors we cannot see", as put up at end of day for a review--what did the students take away from this activity?
- After reading, ask students to predict which telescope is used to look at different objects, using the information on temperature of each, and the range of photons the telescopes are sensitive to. (observatories energies)