Radio signals can bounce back down
Signals come back in the sun...
Radio signals usually travel in a straight line, but not always. Some types of signal bend when they are high above the ground.
If they bend enough, these signals come back down to the ground. They can be received a long way from where they were transmitted.
Slinky signals
... but not in the dark
Special gases at the top of the atmosphere make these radio signals change direction. Sunshine gives these gases more strength, so the signals are bent more in the daytime.
During the night, the gases lose their strength, and only bend the signals a small amount. They will not be bent enough to come back to the ground, and will keep going into space.
Night escape
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