5-8

G3: Compare and contrast the distances and the time required to travel those distances on Earth, in the Solar System, in the Galaxy, and between galaxies.

Organizing Questions	Compare the time required for a spaceship to get to the Moon and to Mars. Compare the time it takes for the Earth to travel around the Sun and Jupiter to go around the Sun. Draw a scale diagram of the planets in the Solar System. Use lightyears and astronomical units to describe distances inside and beyond the Solar System. Would it take more than a human lifetime to travel across our Milky Way galaxy?
Elaboration	Students [in grades 6-8] should pay increasing attention to matters of scale. ... Benchmarks pg. 63 The sun is many thousands of times closer to the earth than any other star. Light from the sun takes a few minutes to reach the earth, but light from the next nearest star takes a few years to arrive. The trip to that star would take the fastest rocket thousands of years. Some distant galaxies are so far away that their light takes several billion years to reach the earth. People on earth, therefore, see them as they were that long ago in the past. Benchmarks 4A2
Specific ideas	Figuring out and contructing models of size and distance - for example, of the plamnets within the solar system - is probably the most effective activity. ... Everyone should experience trying to fashion a physical model of the solar system in which the same scale is used for the sizes of the objects and the distances between them (as distinct from most illustrations, in which distances are underrepresented by a factor of 10 or more). Benchmarks pg. 63 Some experiences with how apparent positions of objects differ from different points of observation will make plausible the estimation of distances to the moon and sun. Finding distances with scale drawings will help students to understand how the distances to the moon and sun were estimated and why the stars must be very much farther away. (The dependence of apparent size on distance can be used to pose the historically important puzzle that star patterns do not appear any larger from one season to the next, even though the earth swings a hundred million miles closer to them.) Benchmarks pg. 63
Developmental & Instructional Implications	Students should add more detail to their picture of the universe, pay increasing attention to matters of scale, and back up their understanding with activities using a variety of astronomical tools. Student access to star finders, telescopes, computer simulations fo planetary orbits, or a planetarium can be useful at this level. Benchmarks p. 63 Using light years to express astronomical distances is not as straightforward as it seems. (Many adults think of light years as a measure of time.) Beginning with analogs such as "automobile hours" may help. Benchmarks pg. 63
Examples

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