UFOs, satellite arrays, the Klingon language, crop circles, and Area 51 can all be found in the Aliens! series (6 titles). Each themed volume contains 12 topical double-page spreads full of trivia, photos, and numbers-driven stat boxes. While Alien Sites features famous locales, like Area 51 and Roswell, and some homegrown operations, such as South Carolina's UFO Welcome Center, many of its entries feel tangential. For instance, the book highlights the Denver International Airport's purportedly cursed statue and rumor-sparking renovations. Though all the books include information on alien theories or sightings that have been debunked, none of the volumes defines UFO or separates it from aliens. That's not necessarily a criticism, but this browsable series is definitely tailored to alien enthusiasts rather than skeptics.