We launched under a warm, cloudless sky heading into a waxing, crescent moon hanging in the western sky, a perfect night for observing the Earth's UV glow. The payload flew west and landed among rattlesnakes near the small Texas town of Stiles. There have not been many measurements of the UV nightglow background, Barbier said. Most scientists have concentrated on measuring the dayglow instead. Nightglow is less intense than dayglow, and sensitive instruments are needed to accurately measure it.
Cosmic rays are atomic particles flying nearly at light speed, constantly bombarding the Earth.
Lower-energy particles come from the Sun. What is most perplexing are the highest-energy cosmic rays. Not only is their origin unknown, these particles possess an energy level that seems implausible. Anything that energetic had to have come from within 150 million light-years of Earth, because anything traveling farther would have lost its energy during the long trip. Yet there are no obvious sources within 150 million light years that could produce a particle this energetic.