What does a blue cloud mean?

What are some problem with microgravity? How does the intensity of a spectral line yield information about the source of the light? How were the hymalayas formed? How many girls have been to space? What holds things in outer space? How does the moon effect the earths ocean? What shapes are most lunar craters? The daylight period in the Northern Hemisphere increases before this date and decreases after it? Why are skyscrapers covered in glass? Why are ionization nebulae found near hot massive stars? How does temperature change as you go up the atmosphere? What is the maximum salary for an astronaut? Why would a 100-pound person weigh only 17 pounds on the Moon? How many times does the Doctor say 'allons-y'? Which invention helped sailors navigate using stars? How much time dose Saturn take to complete one revolution? What clouds form between 2000 m and 8000 m in altitude? What is the name of the space shuttle that shuttled crew to and from their jobs in space? How many days does it take from a new moon to a full moon? How far away is the star Heze?