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I am living in the northern hemisphere in Greece and in class 4 area (light pollution scale).Is it possible to see the Andromeda galaxy with a naked eye?

I'd never heard of a light pollution scale before. How does the scale work, and if I wanted to gauge or estimate my own area, can I do that by looking at objects in they sky visually?

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Only the original poster can answer what was meant, but one system for rating the darkness of the night sky is the Bortle Scale.

https://en.m.wikipedia.org/wiki/Bortle_scale

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  • $\begingroup$ Excellent, this is exactly what I needed to know! $\endgroup$
    – uhoh
    Commented Aug 10, 2018 at 12:09
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As JohnHoltz said, only the OP of the linked question can answer definitively. Chances are, they are referring to the Bortle scale, as that is the most common one you will hear of.

There is also the NELM method (Naked Eye Limiting Magnitude) that classes the darkness of the sky by the faintest star you can see with the naked eye.

There is also the Antoniadi Seeing Scale. Both this and the NELM method can be seen HERE.

the problem with these are that people have different eyesight. Some people can see much fainter stars than other with a naked eye. This means these methods can be good for a general idea only.

Additionally, you could always purchase a SQM (Sky quality meter) which is a small, portable battery powered device that you take out to your dark sky site, point it at the zenith, and the screen will display the darkness of the sky. Do beware that the SQM measures in 'magnitudes per square arcsecond' which means the higher the number, the darker the sky.

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