Meaning a lunar eclipse, when the moon passes between the sun and the earth. It's said in the Prophecy, when all three pieces of L'Eclipser are found, a "shadow will fall upon the world of men". All three pieces together create a sacrificial knife that is used to make a "shadow" fall onto Liveside, so Mike (now Shadow Man) can destroy each member of "The Five", while collecting all the Govi in Liveside as well.
The three pieces are:
So essentially, Mama Nettie is controlling the lunar eclipse to cause night with her voodoo powers for a long period of time, until Shadow Man rids the world of "The Five". The three pieces are just items in the game and don't serve as weapons.