To solve this visual problem, our visual system relies on different cues that help us make sensible guesses about the value of X and Y. To see a large cactus miles away, we must look through an atmosphere filled with dust and moisture. The haze blurs fine details in the cactus. So if we see a great deal of detail, the cactus is not likely to be very far away. Of course, this is only true in the presence of an atmosphere. When we travel in outer space, void of air, atmospheric blurring does not occur. Astronauts have a little harder problem than earthbound people. Even on Earth's moon, which has no atmosphere, we cannot rely on atmospheric haze to help us determine distance.