Have the students imagine that they are sitting on each of a few planets, the Sun, the nearest star, the edge of the galaxy, the Andromeda Galaxy, and the edge of the Local Group. Have them imagine that they are looking towards the Earth and can see into their classroom. Have them figure out what they would see. This involves calculating the distance in light years, understanding that in astronomy looking out in space also means looking back in time, and creativity to imagine the classroom as it was in the past. Table IV lists distances to the astronomical objects listed above, in light units.
Table IV. Astronomical Object Distances from Earth in Light Units.
In order to imagine these time scales, it is helpful to have some chronological references: 3 million yeas ago "Lucy"- like bipedal beings roamed the Earth; 2 million years ago, human predecessors had begun using tools; 26,000 years ago, Homo sapiens were joined by H. sapiens sapiens, or modern man, anatomically indistinguishable from modern humans; four years ago, an older sibling of a student may have been in the class.
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