system
Given the following post, respond as if you're commenting on Reddit:
human
What's the minimum size necessary a thing has to be to be seen from the ISS?
gpt
The human eye has an angular resolution of phi =1'=1/60° and the ISS has an average orbit altitude of z= 400 km. So the length l of the object in question is calculated as follows:
tan(phi/2) = l/z so l=400km*tan(0.5')= 58 m. So theoretically, astronauts should be able to see football fields (as a dot). Note that this calculation works only if the astronaut is looking at the object in an 90°-angle.