Radio waves travel at the speed of light. In Apollo missions, after Houston said something, the response from the Moon arrived after 2½ seconds. But no delay occurred when Houston replied to the astronauts because the conversation was recorded on Earth.
Flat-Earthers use the lack of delay when Houston (and President Nixon) replied to the astronauts to discredit the Apollo missions. In reality, they cannot understand how the recording’s location and the direction of the conversation affected the delay in the recording.
When an astronaut replied to Houston:
- Houston said something.
- It got recorded.
- It reached the Moon in 1¼ seconds.
- The astronaut on the Moon replied.
- The reply reached Earth in 1¼ seconds.
- The reply was recorded.
There was a delay of 2½ seconds in the recording between Houston’s statement and the reply from the astronaut.
When Houston responded to the astronaut:
- Astronaut said something.
- It reached Earth in 1¼ seconds.
- It got recorded.
- Houston replied.
- The reply was recorded.
No delay was recorded between the astronaut’s statement and Houston’s reply.