----Speed of light
Most people usually think of the speed of light as being really fast. It's 671 million miles per hour. That seems tantalizingly zippy if you're caught in traffic.
However, once you think about the speed of light within the context of our solar system, it starts to seem unimpressive.
It takes about 1.3 seconds for light or radio waves to reach us from the Moon, which really isn't all that far away (it's only 20 times farther away than Australia is to the United States). This was an issue during the Apollo space program, because due to the round trip time of the radio signals, NASA had to wait about three seconds to hear the answer to every question they asked the astronauts