"The aim of science is not to open the door to everlasting wisdom, but to set a limit on everlasting error" wrote the playwright Brecht, capturing an important essence of the scientific enterprise. The ability to demarcate astrology from astronomy seems at first glance an easy challenge. However, a complete algorithmic description of the scientific method has eluded both scientists and philosophers, and to this day there is no consensus on the exact nature of scientific inquiry. So how do we tell science from nonsense without a clear definition of science? I will discuss some the issues that have hampered philosophers in defining science and then explore criteria that have been proposed (and used in important court cases) to demarcate science from nonsense. Bring your favorite pseudoscience and see if we explain exactly why it should not be taught in a science classroom!