On January 12, 1980, it was Saturday. The day of the week on January 12, 1979 was -

To solve this, we look at the number of "odd days" between the two dates. Since we are moving from January 12, 1980, back to January 12, 1979, we are traversing exactly one year.

Although 1980 is a leap year, the "extra day" (February 29) falls after January 12, so it isn't counted in this specific interval; therefore, we only subtract 1 odd day (365 days = 52 weeks + 1 day). Subtracting one day from Saturday gives us Friday.