I don't see anything unless you mean that big round glow which if you didn't put it there will be an orb which is atmospherical.
A particle of dust floating towards the ground in close proximity to the lens reflects light into the lens creating an 'orb'. The reason it does not appear on the other photos is that by the time you take them the dust has floated down and out of the frame.
http://en.wikipedia.org/wiki/Orb_(photographic)
div>
explains it pretty well
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