Here is an "optical" illusion that I was shown on a roof of Paris during my studies in cognitive sciences, and that I've never seen elsewhere.

1) Go to a roof or a hill or anywhere you can see a landmark that is at least one kilometer away. If it is a roof, choose a large one, with barriers, because you'll have to walk with your eyes closed !

2a) First let's check how good you are at pointing towards near objects. Choose an object near you, at your hip's height. Stand so that it is at your far right, a bit in front of the line made by your shoulders. Point at it with your right arm. You should have your arm in a "natural pointing attitude", you should not think about it (yep, a bit like if you were someone from the audience taking part in a cumberlandism stuff...)

2b) Close your eyes and walk four steps, while keeping your arm pointed to the near object. At the end of the walk, you should be pointing a bit behind you.

2c) Open your eyes and look down your arm. Very good ! You're indeed pointing at the object with a good precision.

3a) Now, repeat the experiment, but instead of pointing at a near object, point at the landmark far, far away, and place yourself to have the same starting position as in 2a).

3b) Same as 2b)

3c) Open your eyes... Surprise !

.
.
Well I don't know how to make spoilers or to hide the text, so don't read further if you want to try the experiment first
.
.

You should be pointing nowhere near the object : while the correct "solution" is to actually not move the arm at all during the steps - at such a distance, the angular motion is infinitesimal -, you'll move it as if the landmark was 30 or 50 meters away from you. This means our brain simply does not handle correctly the large distances.

This is similar to driving at night while watching the moon (instead of the road.) You are zipping along and the moon is too, keeping the same pace. All the other objects in the area are zipping by in the opposite direction!

Clever!

I'll give this a go cheers, Jc

Great post.

I can't wait to try this later today. It does make sense though!!