Summary
I was able to look at the skybox peripherally through chunks using a high field of view, possibly because of chunks not loading behind your character. I was at the edge of two chunks.

What I expected to happen
I was looking at my crafting table (3 diagonal blocks away) and I expected everything to be normal.

What actually happened
I noticed something out of the corner of my eye as I did this, something black as I moved my cursor around. I was originally at a fov of 90, (Pic where skybox was in the right bottom corner) Then I turned it up to quake pro fov (skybox is in left side of screen) I could see half of the skybox pretty well.

Steps to reproduce

This one is pretty specific, but I managed to recreate it
Step 1: Go to the edge of a chunk
Step 2: Create a box inbetween chunks, the box doesn't have to be a specific size, and can just be 3X3X3 inside. (Bug cannot work if there is natural sunlight coming from the chunk which you are in and looking at.
Step 3: Line yourself up at the tippity edge of the chunk with one block of the box empty behind you (Which is in a different chunk)
Step 4: Look left diagonally to a block three blocks away on the floor on the right corner of it.
Step 5: Bug should work

If you look at the left corner of the block (When looking diagonally left) Or the right corner (When looking diagonally left) OR you move into the chunk behind you, the bug stops. The bug isn't sensitive to gamemodes.

Notes: The original pictures show the sun and moon because I could see the skybox eastward and westward while looking north/south. So note that it could work the other way. This should be looked into for more than the bug I just showed, as there could be weird interactions at the intersections of 4 chunks.

Exploitative uses: This fits a niche role, the worst thing that could happen is someone mining could tell what time it is without a clock by closing up the cave they are in and using F3 + G to find a chunk boundary. Honestly I am surprised this hasn't already been found. I guess it is just a very niche situation I have stumbled upon.

Good luck in fixing this!

EDIT: The picture of the box with the lime green wool is not only proof that it can be recreated in 1.11.2 (the other ones were in snapshot 1.12-pre5), but that you can see the skybox northward and westward while looking east or west.

-lumpypudding

And to whom it may concern I was on graphics:fancy, clouds:fancy (I don't know if it matters but if it does I will post more details)
Whelp, a duplicate Hope I could have provided more detail about this bug.