Its basically a pixel that has died on the CCD? i think, and appears as a blue or red dot in the picture. It only appears in long night time exposures and my daytime shots are unaffected.
Thanks for the comment.
Nice photo Craig...

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..tell me about dead pixels...

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I've got 4 of them on my LCD monitor, (the max allowed by Philips)....!
One of then looks like a sparrow constantly flying in the sky front of me in the flight sim.... ::)...

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..bleedin nuisance...

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LOL...!
Paul.
Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.