6 January is Old Christmas. This is Christmas day by the Julian Calendar.
The Julian Calendar was developed circa 30 BC and became, more or less, standard by 8 BC. The Julian Calendar had errors and over time was less accurate.
In the late 1500s it was a problem and Pope Gregory XIII changed the calendar to make it match the solar cycle. The Pope and his advisors, did this by eliminating 11 full days and thus created the Gregorian Calendar.
Several countries did not accept this calendar change, notably the Isles did not. Ireland, Scotland, Wales, and England, continued to use the old Julian Calendar. Finally, given that the calendar was hopelessly wrong, the crown adopted the Gregorian Calendar in 1752.
In the 1700s many thousands of Irish, Scots, Scots-Irish, and
English, were settling in the Colonies. Many of these people, the Anglo-Celts,
lived on the frontier. Some did not know of the calendar change and some flat
out refused to use the new calendar, so for many early Americans Christmas Day
fell on 6 January rather than 25 December. By the 1800s most people accepted
the new calendar and used it, a few did not.
In the Southern Uplands and Backsttlements, some people continued to use
the Old Christmas, as they felt it was the real Christmas.
Even in the 20th Century some people still kept the
Old Christmas. It was my grandmother
McCain that told me about the Old Christmas and she kept it and the new one,
meaning she observed by 25 December and 6 January, as Christmas. I always liked that. I am keeping up the tradition and I also keep
both Christmases.