"Kattegat" is not the name of a place, but of a sea-straight between Denmark and Sweden. Moreover, the name isn't Danish. The sea-straight was named so by Dutch sailors many centuries later. It literally means 'cat hole' and refers to a narrow passage.
The Northern lights cannot be seen anywhere near Kattegat, which lies outside of subarctic zone.
The Vikings' "Chieftain" says they will raid "Russia". Russia wasn't called "Russia" back then. Vikings called the Novgorod Republic "Holmsgaard". To the rest of Europe it was known as "Kaganate".
The dog Ragnar has is an Scottish Deerhound, a modern breed which did not exist until the 19th century.