Day of the week calculation

2004 was a leap year. Therefore, from $8^{\text{th}}$ February 2004 to $8^{\text{th}}$ February 2005, there are 366 days.

Number of odd days = $366 \pmod 7 = 2$.

Since $8^{\text{th}}$ February 2005 is Tuesday, the day on $8^{\text{th}}$ February 2004 was Tuesday $- 2 \text{ days} = \text{Sunday}$.