This book introduces readers to famous UFO sightings, revealing what the legends claim, some possible explanations, and what people still don't know for sure. Short paragraphs of easy-to-read text are paired with eye-catching images to make reading engaging and accessible. The book also includes a table of contents, fun facts, sidebars, comprehension questions, a glossary, an index, and a list of resources for further reading. Apex books have low reading levels (grades 2-3) but are designed for older students, with interest levels of grades 3-7.