How is hydrogen used in a hot air balloon?

What planet appears to be blue-green when you look in a telescope? Who invented the first lunar module? What are the four most abundant components of the atmosphere? When was the Andromeda Galaxy discovered? How high is Dallas above sea level? What are seasonal star positions? What position is the Northern Hemisphere receiving the most hours of sunlight per day? What was the name of the early space program? What is the shape of Jupiter? How did the planets start? Where will you go if you circumnavigate our planet? What planet's temperature range from -13 Celsius to 37 Celsius? When was Sun Sun created? Length of a yeaR ON Mars? Some constellation such as Ursa Minor are visible in the sky year-round other constellations appear for only part of the year? How do use cloud in sentence? Why is mars called earth's sister planet? What is a space cadet? What are Buzz Aldrin children doing now? When was NASA Exceptional Service Medal created?