A Monday. Source: http://www.hf.rim.or.jp/~kaji/cal/cal.cgi?1959
Friday
Thursday
September 1st 1959 was a Tuesday.
September 8, 1959 was a Tuesday.
15 September 1959 was a Tuesday.
24 September 1959 was a Thursday.
September 13 1959 was on a Sunday.
September 10 in 1959 was on a Thursday.
September 1 1959 was on a Tuesday.
September 23rd 1959 was a Wednesday.
September 9, 1959, was a Wednesday.
September 30 1959 was a Wednesday.