Wednesday, 21 November 2012

Moving shadow ghost vanishes!

Shadow ghostLooking out of a window at a wet urban night scene recently, I saw two small 'shadow objects' on a road surface. They moved for a while and then vanished. The whole sighting lasted for just a second or two! I continued to look for a while but they did not reappear, nor was there any obvious clue as to what they were! Unlike most shadow ghosts, these were not in peripheral vision and the lighting, provided by street lights, was good! I've never seen this variety of shadow ghost before and was intrigued!

When nothing else happened, I looked in another direction. On returning my gaze to the place where I saw the shadows, they were back! Again, they moved a little and then vanished. Some experimentation revealed some interesting properties of these shadow objects. Firstly, they moved as my gaze moved! Secondly, they appeared reliably AFTER I stared at another scene for a while and then back. That's when I realised they were a type of afterimage.

Most people are familiar with afterimages. These happen when you gaze for a while at a bright object, then look away and see an impression of it (often in a different colour) superimposed on whatever you're now looking at. In this case, I think a bright streetlight was reflecting a puddle and, when I looked away, it became a 'shadow object' in another scene. You can often tell for sure that you are looking at an afterimage because it usually is still visible even when you close your eyes. Also, it moves according to wherever you happen to be looking, unlike a real object in the scene.

In most situations afterimages are obvious. If you stare at a brightly lit pattern and then seen the same pattern superimposed on the next thing you look at (often in a different colour), it's not going to make you think it is paranormal! But in the particular situation here, an essentially black and white scene with some areas well lit by street lights, an afterimage may not be so obvious. I believe I was seeing the dark afterimage of a bright puddle reflecting a street light. This appeared as an amorphous black shape when seen on a modestly-lit bit of road surface. They moved because my gaze moved and they vanished as the effect wore off.

When it is not obvious what is causing an unusual effect, like these 'shadow objects', some people might consider them paranormal. Though most shadow ghosts are reported in peripheral vision, some are seen in central vision. I wonder how many may be caused by afterimages like this? It is certainly something to consider when shadow ghosts are reported in mostly black and white scenes.

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