9-12

G3: Explain how astonomers measure interstellar distances.

Organizing Questions	Explain what a lightyear is. Discuss the principle of parallax and explain how it is used to measure the distance to a star. Describe how the properties of variable stars (Cephids) can be used to measure interstellar distances.
Elaboration	There is no specific mention of measuring interstellar distances in the national documents.
Specific Ideas
Developmental & Instructional Implications	This is the time [grades 9-12] for all of the pieces to come together. … The scale of billions will make better sense, and the speed of light can be used to express relative distances conveniently. Benchmarks p. 65 The range of numbers that people can grasp increases with age. No benefit comes from trying to foist exponential notation on children who can't grasp its meaning at all. It has been argued that people really can't comprehend a range of more than about 1,000 to 1 at any one moment. One can think of a meter being a thousand millimeters (they are there to be seen in a quick look at a meter stick) and that a kilometer is a thousand meters (it can be run off in a few minutes)--but one may not be able to think of a kilometer as a million millimeters. A million becomes meaningful, however, as a thousand thousands, once a thousand becomes comprehensible. Particularly important senses of scale to develop for science literacy are the immense size of the cosmos, the minute size of molecules, and the enormous age of the earth (and the life on it). Benchmarks pg. 276 Increasingly sophisticated technology is used to learn about the universe. Visual, radio, and x-ray telescopes collect information from across the entire spectrum of electromagnetic waves; computers handle an avalanche of data and increasingly complicated computations to interpret them; space probes send back data and materials from the remote parts of the solar system...Benchmark 4A3
Examples

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