Shadow stretching

General Questions
#1

This morning I saw my shadow stretch, almost as if it were a special effect from “The Matrix”. I’ll try to describe.

I was standing in a doorway with the sun directly behind me. It was about 7:30 AM, so the sun was fairly low in the sky. Looking forward and down I could see the shadow of the doorframe, and my own shadow next to it.

When I went to lean on the door frame I noticed that the perimeter of my shadow appeared to stretch sideways to meet the shadow of the door frame. Almost as if it were being sucked toward it.

I searched around for another light source, but there was none. The effect was very pronounced at my head, but hardly noticeable at all at my feet (remember, the sun was BEHIND me). So I’m guessing this has to do with length of my shadow, and the relative angles from which the sun was shining on the various parts of my body.

Can anyone explain this effect? Or am I entering the Matrix?

#2

Wow, sounds exactly like a calculus problem. (What is the rate of change of the top of the shadow, when his right shoulder is one inch from the door frame?)
But yes, from what you describe it has to do with the angle of the sun and the way you were leaning.

#3

There was a thread on this that I can’t find. It might have been before the meltdown.

[WAG] Shadow edges always have a diffraction band and are fuzzy even when they look sharp. The diffraction bands of the two shadows close together merge as the objects get close to each other.[/wag]

#4

There was a thread about this a while back and, although various hypothese about diffraction were put forward, I think the general conclusion was something like this:

The sun isn’t a point source, so your shadow isn’t sharp-edged (although it looks it), neither is the shadow of the door frame - it consists of a region of total shadow (ignoring other sources of illumination), bordered by a fringe of graduated partal shadow. When the shadows move close to one another, the fringes (which you may have been perceiving as ‘non shadow’) overlap, forming a darker region that, perceptually, appears to ‘stretch out’ from one side to the other.

#5

I just tested this in a drawing program by making two circular objects with a gradient fill from centre(black) to edge (transparent) and by moving one over the other, they both appeared to ‘stretch’ out toward one another.

#6

And wouldn’t the hair on your head make the shadow less defined, explaining why it (stretching) was more pronouned with your head’s shadow?