For a European the "l'heure bleue" is something around sevenish in Paris when you take a drink before dinner.
If you look at the optical phenomena when the sky is very blue it depends very much on time of the year and
how high north you are. At the polar circle level it can happened around midnight in the summer and and at
Christmas time it prevails all day. My contributions is not coming from the classical time of day.
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Close to Polar circle around 24:00 in July
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South Sweden early May at 21:30
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South Sweden early Jan at 16:00
Excuse the rambling
Mats