For most of human history, nighttime meant deep darkness. But today, the majority of the world's population no longer experiences a truly dark and starry night. For his book, "The End of Night," author Paul Bogard traveled to the world's few remaining naturally dark places, like the Sahara Desert. We'll talk to Bogard about his book, and find out about the National Park Service's Night Skies program, which seeks to curb light pollution.