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?
Assuming you mean Bortle class 4, then the Andromeda galaxy (M31) should be a fairly easy object with the naked eye. It won’t be particularly impressive, but rather will look like a hazy blob. On the other hand it is more than 2 million light years distant, so it’s impressive to be able to see it at all.
Yes, you can see Andromeda with the naked eye, assuming you have a site with suitable dark skies. Under good seeing conditions, you should be able to see it as a bit of a small hazy area using averted vision even in suburban skies.
Going a bit further out to a site with a good dark sky, you should be able to see it when looking directly at it.
Greece is (approximately) located around 40°N to 36°N in latitude. Andromeda galaxy is at +41° declination (approx).
Using this information, you can see how high it will rise in the sky (in the best scenario) which is important because if it is too low on the horizon, it will be extremely difficult to see. By using the formula (90°-latitude)+declination, we can see that Andromeda Galaxy will get to just over 90° from your horizon, (at the best case, being in the Northern part of Greece)) which means it will be almost directly overhead! Obviously, this is an approximation because the earth does have an axial tilt! Either way, this shows that it will get far clear of the horizon, meaning less atmospheric distortion. Of course, it would be best to do it when it is 90° above the horizon during the night time!
Download one of the many free apps you can get on your phone which will tell you the best times to view it.