why tonight's full moon is a 'harvest moon' lunar eclipse

Tonight is a traditional "Harvest Moon."  The moon is also at its closest point to Earth, so it is sometimes called a "Super Moon" (though it won't appear much bigger than usual using the naked eye).  And, the moon will have an eclipse as seen from the US.  For more information, check out:

http//www.space.com/30668-harvest-moon-lunar-eclipse-name.html