During a rainy hike canyon walls are visible from the bottom (although a bit foggy). However, when I got to the top, I couldn’t see the bottom anymore—everything was just white. Can someone explain like I’m five why the top is visible from the bottom, but not the other way around?
Edit: missing detail, the weather didn’t change throughout the hike. An the Bailong Elevator led to the top so we reached it within a minute or so. When going down by a cable car the canyons became visible again.
In: Physics
The fog handles the sunlight differently depending on your viewing angle.
From up above the sunlight is bounced back at you obstructing your view
From below the sunlight is dissipated which does not block your view
Think about it like being underwater. You can look up and see through the surface, but if you were looking from above the surface down, the sun’s glare blocks your view.
Another analogy: a thin lace curtain or mosquito net can block people from looking into a room, but from inside the room you can still see out.
There’s a couple factors.
First, we have to remember that *everything* you see is because light bounces off of it and into your eye. When you see an apple, it’s because light from the sun hits it, and the red light bounces off the apple and goes into your eye.
Also, your eyes adjust to the ambient brightness. Ever tried looking into a dark window on a sunny day? You have to shade your eyes to see anything inside, right? When you’re in the canyon, the sky and everything above is the brightest thing, so it’s easy to see clearly. When you’re outside the canyon, the bottom of the canyon is relatively much darker, so it’s already harder to see
clearly.
Another thing is to consider the path of the light. To see something outside the canyon, for example the canyon walls, from inside the mist at the bottom, you need light from the sun to bounce off of the rock, avoid the misty water particles, and then bounce into your eyes.
To see something inside the canyon from outside, you need light to come from the sun, avoid the mist, bounce off the bottom of the canyon, avoid the mist again, and bounce into your eyes. So it basically has to pass through the mist twice, giving it double the chance to get scattered or absorbed before it reaches your eyes.
Also, a lot of the light bounces *off* the mist particles. When you’re outside the canyon, the light bouncing off the mist can block the light bouncing off the bottom of the canyon, so you only see mist. When you’re inside the canyon, since the light is all coming from above, you don’t see much of the bounced light from the mist. All the light that reaches your eyes has basically passed through the mist, making the mist look mostly transparent.
When you’re at the bottom of the canyon looking up, you can see the top because the fog is usually denser at the bottom and lighter as you go higher, allowing you to see through the lighter fog to the top. When you’re at the top looking down, the fog is thicker below you, blocking your view of the bottom and making everything look white.
Latest Answers