The almanac has a perpetual calendar from 1900 to 2100. There are only seven possible days of the week for January 1, and there are a few more pages for leap year. The list of years tells you which calendar pages to use.
What day of the week was August 11 1990
August 9th, 1979 fell on a Thursday.
May 9th, 1990 fell on a Wednesday.
The 9th of August can occur on any day of the week. As the question was asked in July 2014, it is possible you were referring to August of 2014, in which case the answer is Saturday.
It was a Friday.
Friday
its on a Monday!
Thursday
Tuesday
It was a Monday.
Tuesday
Thursday