There was disappointment early Tuesday evening as members of the Delaware Valley Amatuer Astronomers setup their telescopes in a parking lot at the King of Prussia Mall to watch the planet Venus pass in front of the sun. Cloudy skies kept them from seeing the extremely rare transit. But while the transit wasn't visible through the telescopes because of the clouds, it could still be seen online on an I-pad that a group member brought along just in case. It will be more than 100 years before the next transit of Venus. They are rare because the orbits of Earth and Venus are not in the same plane so from our point of view it usually appears that Venus either passes above or below the sun.