When does a Day Begin & End?

	Article Title
1	What about Nehemiah 13:19? It gives support to sunset to sunset day length.
2	If the Biblical Sabbath is only 12 hours long (Christ said, "Are there not 12 hours in a day?") then how long is your Sabbath if you live in the Arctic Circle? Is it still the standard 12 hours? Or 18? 21?
3	When does Scripture say a day begins?