Its all about shadows and the size, in this case the Earth and the Moon. First, the solar eclipse. When a solar eclipse occurs, the moon blocks the sunlight from the sun, casting a shadow on the Earth. Well, the moon is only a third of the size of the Earth, so, the shadow casted by the moon into the Earth is quite limited. However, during a lunar eclipse, this time, the Earth blocks the sunlight away from the moon, casting a shadow on the moon. Since the Earth has three times more size than the moon, the shadow casted by the Earth to the moon is far larger than the moon on the Earth during a solar eclipse. More shadow area means longer eclipse and less shadow area means faster eclipse. This is why the lunar eclipse takes longer than the solar eclipse.
