[necovek]

You've got two approximations we are used to working with.

One is our eyesight, which is pretty precise (error depending on the speed of light) — of course, I am not getting into all the potential ways our eyesight can fail us.

Another is our stereoscopic sound positioning based on having two ears, which is ultimately much less precise, but can still point in a general direction of where the sound you are hearing right now is coming from. If you've got both functioning ears, you can usually tell if someone is calling you from the front, either side or from the back. Some people are better at it than others, though.

Sound you are hearing right now (a discreet event) has been emitted at a particular point by an airplane a number of seconds/minutes away — this is what identifies the "discreet" point and requires no remarkable event like an explosion, and you can do the math based on that and the two "instruments" you'd use. I am not sure why would it matter that airplane produces the sound continuously for discussing this discreet moment in time when a particular sound was produced? (unless you are going for there being no vibration of air possible without time passing, which is needlessly picky).

[dTal]

Excellent post, however the word you likely mean is spelled "discrete" - a "discreet" event would be hard to hear :)

[necovek]

Indeed and LOL, thanks for the correction :D