Not sure that the Gregorian calendar that we use works back that far, but if it did, it would have been a Friday.
August 9th, 1979 fell on a Thursday.
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.
Thursday
its on a Monday!
Tuesday
Tuesday
It was a Monday.
Thursday
August 9th 1986 was a Saturday.
August 9th 1998 was a Sunday.
August 9, 1959 was Sunday.
August 9th, 2009 fell on a Sunday.