Seeing stars

A spacey kind of activity that demonstrates how the Hubble Telescope sends images of celestial bodies to earth

The reconfigured Hubble Space Telescope has been producing incredible high-resolution pictures of celestial objects that are superior to any produced by a land-based telescope. The Hubble will remain in space for years, capturing light from distant objects and radioing images to NASA scientists on earth.

The images are transmitted byte by byte in numerical form (binary code) to waiting computers that store the data and interpret the numbers used to reassemble the images into high resolution photographs.

No way you're going to duplicate the imaging process in a classroom, of course. What you can do, though, is demonstrate in simple terms just how the process works. (This activity, by the way, is adapted from an activity created by the Exploratorium, San Francisco, CA)

You'll need the following: a slide projector; a color slide of a clearly defined object, such as Saturn, a building or your school; one flat, white dowel rod, 1/2" x 36"; a sheet of white paper; and a dark room.

Four steps. With your materials on hand, you're ready to stage the activity. Here, step by step, is what you do:

1. Set up the slide projector in a dark room (I recommend a gymnasium) and focus a recognizable image of a slide at a distance of about 20 feet.

2. Hold up the sheet of paper in the beam at the proper distance for focusing. Be sure the focus point is in the middle of the room. If it's near a wall, the image will be easy to make out (which is not what you want to happen).

3. Hold the white dowel rod in one hand, and slowly move it up and down, perpendicular to the projector beam at the focus distance. Ask the students to try to make out the picture.

4. Gradually increase the speed of the rod's movement. When the rod is moving very fast, the image will become very clear.

How it works. This activity demonstrates the imaging process used by the Hubble Space Telescope. By slowly moving the rod across the projector's beam, at a point where a projection screen is usually located, small fragments of the image are captured and reflected ("radioed") toward the students.

Because the fragments are quickly forgotten, the addition of many more fragments, as the rod continues to move, confuse the image in the student's mind.

However, as the rod is moved more rapidly, an important property of the eye comes into play. Light images are momentarily retained on the retina of the eye. This property is called "persistence of vision." As the rod is moved rapidly, each image fragment remains just long enough to combine with other fragments to form a recognizable image.

In this activity, the eye is an analogy of the image processing computer that stores numerical image fragments - collected and radioed to earth by the Hubble Space Telescope - and reassembles them for use.

John Cowens teaches fifth grade at Fort Vannoy Elementary School, Grants Pass, OR.

Copyright Early Years, Inc. Jan 1997
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