Sophie could hear something about an equation, but that went over her head. So she just kept on moving--that is, until she heard the word STOP. She stopped in place and turned to face the professor. They were only a third or fourth of the way to their goal? What goal, and why was it taking so long to get there? Now the professor was talking about ten kilometers and why it was so significant.

Could Sophie tell him why? Uhh, no.

Then it occurred to her. What in Astronomy took a really, really long time? A lot of things did, but they were traveling, which meant the answer might have something to do with--"Is it a light year?" she asked, raising her hand. "Or, does it take a whole bunch of those kilometers to equal light year?"