Step 1: Understanding the Question:
We are given that January 12, 1980, falls on a Saturday.
We need to track backwards to find the day of the week for the exact same date in the previous year, January 12, 1979.
Step 2: Key Formula or Approach:
An ordinary year consists of exactly 365 days, which breaks down into 52 weeks and 1 extra day (called an odd day).
A leap year has 366 days, which breaks down into 52 weeks and 2 odd days.
Because an ordinary year shifts the calendar by 1 odd day, going backward one ordinary year shifts the weekday backward by 1 day.
We must check whether the time period between January 12, 1979, and January 12, 1980, includes a February 29th.
Step 3: Detailed Explanation:
We are moving backwards from January 12, 1980, to January 12, 1979.
Let us analyze the year 1979. It is not divisible by 4, so 1979 is an ordinary year.
Even though 1980 is a leap year (since 1980 is divisible by 4), the leap day for 1980 is February 29, 1980.
The period from January 12, 1979, up to January 12, 1980, strictly occurs before February 1980.
Therefore, this specific time frame does not contain the extra day of the leap year.
The total number of days between January 12, 1979, and January 12, 1980, is exactly 365 days.
365 days is equal to 52 complete weeks and exactly 1 odd day.
This means the calendar advances by exactly 1 day of the week from 1979 to 1980.
Since we know 1980 is a Saturday, the same date in 1979 must be exactly one day prior.
One day before Saturday is Friday.
Step 4: Final Answer:
The day of the week on January 12, 1979 was Friday.