December 12 can fall on any day of the week.
March 12, 1978 was a Sunday.
February 12 1978 was a Sunday.
September 12, 1978 fell on a Tuesday.
June 12, 1978, was a Monday.
December 12, 1990 was a Wednesday.
December 12 1947 was a Friday.
December 12 1958 was a Friday.
December 12 2010 was a Sunday.
Thursday
December 12, 1972 fell on a Tuesday.
December 12, 1765 fell on a Thursday.