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Old 18th Oct 2020, 16:57
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old,not bold
 
Join Date: Apr 2006
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Originally Posted by roger4
Strictly, you aren't seeing the Andromeda Galaxy, you are seeing light that left Andromeda 2.5million years ago and has only just arrived on earth!
Yes well, that's true; just as it's true of "seeing" a lighthouse; you are seeing the light that left the lighthouse a short time** ago, not the lighthouse.

** 0.0000166 of a second, roughly. I think, if you're in a small sailing boat and the lighthouse is on the horizon. While the light is travelling towards you your boat will move 0.0000355 of a metre in whatever direction your CMG might be, which is something to take into account when doing a running fix using the lighthouse.
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