Stuart Smith, age 12, of Winston Salem, North Carolina, for his question:

Can beams from radio stations bounce back from space years later?

Radio is a form of electromagnetic energy. Hence it travels in straight lines, fanning out from its source at the speed of light. Like light, its beams can be stopped or absorbed or diverted by solid objects in its path. Its energy spreads out and diminishes with distance but faint signals can be boosted by amplifiers. Like beams of light, it can bounce from a solid surface and reflect back in the direction from which it came. In theory, at least, it would seem possible to beam a radio signal to Sirius and expect its dim reflection to return to earth after about 17 years.

This radio space hopping would be a huge project calling for intensely powerful beams. So far, scientists have been successful in bouncing back a radio signal from the moon and, of course, from our artificial communications satellites. But many stars emit their own radio energy, and our scientists devote long hours to catching and amplifying these celestial radio beams from objects clear across our Galaxy and beyond.