Most evenings I see strange flashes of light in the sky, particularly on cloudy days. Usually if I'm staring at the sky around 9pm-11pm in an easterly direction.

It looks like it is probably a powerful flashlight / laser show from some distance away (possibly the Millennium Dome). Does anybody know the source? Or is it possible that aliens have been hovering over Forest Hill after watching Location Location Location?

In a similar vein, is it really possible that I heard the new years fireworks on the Thames from my house? Once they finished on the TV there was about 15 seconds of loud rumble outside, which died away very quickly. Other displays didn't seem to generate the same level of noise. But it seems like a long way for the noise to travel, including over the Horniman hill.

I get that. For me it is the railway line where it sparks the electric rail when the trains pull out heading south. It had bugged me for a couple of winters then I realised eventually what the cause was. I'm Dartmouth Rd so that explains my bright flashes, not sure where you are though.

It could be the same reason, but it must be a fairly large spark to be seen from the top of the hill. But an interesting possibility.

Could be the Greenwich laser beam? Depending on weather/orangey light noise, it looks more white than green.

http://www.thegreenwichmeridian.org/tgm/...article=14

I think that BMqpr is on the money here.

Arcs from the third rail pickup definitely cause flashes like this. If the clouds are low level then the affect can be quite striking. If there is ice about then this only amplifies it due to the top pickup arrangement. (A poor choice made when the Southern Railway was formed - we are still suffering from this - the LBSC had the right idea).