Named for the Greek god of the sun, Helios, Helium is the second most abundant element in the universe. Scientists discovered helium while they were studying the sun. A colorless and odorless gas, helium is so light it floats in air. At first scientists couldn't decide if helium was useful for anything. Today, helium is extremely valuable and rare, used in devices ranging from medical equipment to laboratory instruments to welding to scuba gear, and...