Did you know that the night sky is alive with all kinds of light that we can’t see?  Radio waves, ultraviolet light, gamma rays, infrared light, microwaves, and x-rays are all used by astronomers.  But wait—doesn’t the greenhouse effect absorb infrared?  And doesn’t the ozone layer block ultraviolet?  How can these reach us?  And don’t x-rays pass through everything?  How do we...