Why don't Eclipse happens twice a Month???

It's not often that we get a chance to see our planet's shadow, but a lunar eclipse gives us a fleeting glimpse. During these rare events, the full Moon rapidly darkens and then glows red as it enters the Earth's shadow. Though a lunar eclipse can be seen only at night, it's worth staying up to catch the show. The next lunar eclipse visible from the western hemisphere will take place in the early morning hours of April 15, 2014, from about 2:00 am - 5:30 am Eastern Daylight Time (EDT).