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Obviously, it cannot be faster than the speed of sound.
So, indeed, if we were at around 200 km, the sound could not have reached us after 4 minutes.
I am 67 years old, and this happens 45 years ago: obviously my memory is failing.

4 minutes at the speed of sound is around 83 km.
We definitely were farther than that.

I am convinced that the 200 km are correct. So the sound must have reached us 10 minutes later, not 4.

Thank you for pointing to my mistake.

interesting

You're good at your calculations...
@pocketechange