40 is the atomic number of zirconium.
The planet Venus forms a pentagram in the night sky every eight years with it returning to its original point every 40 years with a 40 day regression.
"Forty days & forty nights" describes the period for which rain fell during Noah's flood.
The code for direct dial international phone calls to Romania is 40.
"Afterward, when they had stopped for a moment to allow Tip to rest, they saw forty roads branching off from their feet in forty different directions; and soon these forty roads began whirling around like a mighty wheel, first in one direction and then in the other, completely bewildering their vision." from The Marvelous Land of Oz by L. Frank Baum
And this is so good: Rostropovich playing Shostakovich Cello Sonata Op. 40.