Many of the darkest secrets about the U.S. military's post-9/11 covert operations remain hidden from view. But photographer Trevor Paglen aims to unearth them, one art exhibition at a time. Two years ago at the Yerba Buena Center for the Arts, he produced passport images of CIA agents who shuttled suspected terrorists to detention facilities that, officially, didn't exist. He followed up with a book about patches worn on the uniforms of secret military personnel, I Could Tell You But Then You Would Have to Be Destroyed by Me, which revealed the odd names of classified projects like "Goat Suckers" and "A Lifetime of Silence Behind the Green Door." (Paglen thinks that last one might be a reference to a 1970s porn flick.) His recent exhibits at the Altman Siegel Gallery and at SFMOMA might have been his spookiest. Using long-exposure photography, Paglen captured top-secret satellites streaking through the open sky. Beware: Viewing this artwork may pose a threat to national security.