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Astronomy with an online telescope

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Picture of Darran Clegg

Darran Clegg Post 1

4 Jan 2021, 15:33

Night vision.

I know a red torch is recomended, so why are night vision cameras (like the one used in week two) green?

Picture of Alan Cayless

Alan Cayless Post 2 (unread) in reply to 1

4 Jan 2021, 17:32

Hi Darran;

Thank you for this interesting question.  

It really comes down to using different technologies in different situations.  The human eye is most sensitive in the green part of the spectrum, so it makes sense for night vision equipment to relay a possibly faint image in green, as this gives the greatest increase in sensitivity (considering the eye as part of the overall optical system).  Another factor is that image intensifiers originally worked with a fluorescent screen, which would have been green.

The red torch is used in a different situation - where you want to preserve your night vision for looking at the stars (and other faint celestial objects).  Here, using red to illuminate the environment (or your star chart) avoids over-stimulating the eye, keeping your eyes dark adapted for when you look up at the sky.

Alan

AOT_1

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