Friday, 23 August 2013

Now there are TWO ghosts!

ShadowIt seems that my door ghost (door what?) now has a friend! Not that it felt friendly when I saw it! I was the usual position where I see the door ghost and, as is often the case, I wasn't thinking about ghosts. I noticed a shadowy figure behind me but quickly realised, to my surprise, it was a different figure!

The new shadowy figure was a different shape and was in a different position - further back than usual. Given the nature of the door ghost, a misperception, this was somewhere on the road between incredibly unlikely and impossible.

Turning round sharply, I saw that the new ghost was actually an exceptionally dark shadow on the ground, cast by a nearby bush. So why had I never noticed it before? Looking at the shadow, it was clear that the sun needed to be in a particular place in the sky to cast the shadow somewhere I could see it from my 'usual position'. If the sun was a few degrees away in any direction, the shadow would not be visible. The sunshine also needed to be strong to cast such a dark shadow.

I would guess these factors can only occur together for a short period (tens of minutes?) on a small number of days around this time of year. So why didn't I notice it last year or the one before? Well, here in the UK we've had a series of summers with little sun. And I would still need to be in the right position during a relatively short period of time during the day. So the odds have been against noticing this second shadow ghost until this summer.

But here's an oddity! I could not see the usual door ghost at the same time as the 'new' ghost, even though I deliberately looked for it at the time. I think it is possible that these two misperceptions may be mutually exclusive. The reason is that they are caused by objects at significantly different distances from the observer, so requiring a change of focus. In general, though, I don't see why someone shouldn't see more than one significant misperception in their field of view at one time. But I do wonder what the odds are against having TWO shadow ghosts in such close proximity.

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