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Pondering Bortle scale


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According to Clear Outside my local skies are Bortle 4.  Although I live in Norfolk, about 20 miles from Norwich I live in the middle of a new build housing estate, which causes quite a lot of local light pollution.  in a town which seems to have a new estate built every year (old airbase being completely redeveloped). 

My Father house, in the middle of nowhere, in Kent has much darker skies but is also listed as Bortle 4.  

I am confused

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Bortle 4 has magnitude range 20.4 to 21.3. Perhaps you and your father are at either ends of this scale? So have almost 1 bortle difference even though both a 4?  It's better to use the magnitude scale if you can to compare different locations.

That said, you could both have very similar magnitudes too.  This could be because Norfolk is generally a less populated and lower light polluted area than Kent; i.e. you get pollution from your local town and from 1 large city (Norwich) while your father gets no local pollution but lots and lots of pollution from the many and larger towns and cities round and about. So your some + some is similar to his none + lots.

You should really only use published figures as a general guide.  If you observe at both sites you'll soon know which is better in practice.

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