Question

X-rays cannot pass through Earth's atmosphere. Which of these is the best location to place a telescope used to observe x-rays from stars?
mountain
top of building
space
high-flying aircraft

Answer 1

Mountains, tops of buildings, and high-flying aircraft are all part of Earth's atmosphere, no matter how high they are. On the other hand, space doesn't belong to our atmosphere, it is outside of it. Having this in mind, the best location to place a telescope used to observe x-rays from stars is in space.

Answer 2

Space because you are closest to the stars