the unlucky day is Friday the 13th
13th March 1957 was a Wednesday.
August 13th, 1975 was a Wednesday.
It's June 13th, because Valentine's Day occurs just before February the 13th. At least, that's what I think, but you could also argue the opposite point, that February 13th is more unlucky than June 13th, because it occurs just after Valentine's Day (assummed to be lucky), therefore it must be unlucky. Hope this helps!
The 13th
It was a Wednesday.
Wednesday
Wednesday.
Wednesday
Wednesday
September 13th 1961 was a Wednesday.
January 13th 2010 was a Wednesday.