Neil degrasse Tysons documentary series the Cosmos, he mentions that we actually see the moon one second later than it actually is due to the distance of the earth and the moon and speed of light making us see the moon a second behind instead of at real time. If there was someone on the moon clapping (and we ignored other rules of physics like the sound fading and sound waves through space) how long would it take to hear them clapping from Earth?


1 Answer 1


If you are to say: ignore that there exists no medium for the sound wave to travel and calculate the time it would take for a sound wave in some medium (air, for instance) to travel that distance. It would be calculated as follows: Speed of sound in air is $|v| = 343 \frac{m}{s}$ the distance between the moon and earth is about $384.4 \times 10^6$ meters. So distance divided by the speed is $\frac{384,400,000~{m}}{343 \frac{m}{s}} = 1120699.70845$ seconds, about 13 days.

So if there was air between the earth and the moon for the sound to travel and the wave didn't lose energy, you would hear the clapping in roughly 13 days.

  • $\begingroup$ What if there was only one hand clapping? $\endgroup$
    – user95006
    May 24, 2016 at 22:14
  • 2
    $\begingroup$ In that case, I'd have to "give the guy a hand!" $\endgroup$ May 25, 2016 at 0:29
  • $\begingroup$ @user95006 then the question would belong in philosophy. $\endgroup$
    – Willtech
    Oct 20, 2019 at 20:43

Not the answer you're looking for? Browse other questions tagged or ask your own question.