They are big, black, and triangular. In UFO folklore they are proof-positive that planet Earth is a rest stop for joyriding, but road-weary, extraterrestrials.A just released study by the National Institute for Discovery Science (NIDS), based in Las Vegas, Nevada, sheds new light on the dark and mysterious craft. They offer a more down-to-earth hypothesis.NIDS researchers contend that these type vehicles are lighter-than-air, blimp-style craft of the U.S. military's making. Likely powered by "electrokinetic" drive, the lifting body-shaped airships have been skirting the skies from perhaps the early to mid 1980s. NIDS has followed up on their study of...