When people orbit the earth or travel to the moon, they must live temporarily in space. Conditions there differ greatly from those on the earth.
Space has no air, and temperatures reach extremes of heat and cold.
The sun gives off dangerous radiation. Various types of matter also create hazards in space. For example, particles of dust called micrometeoroids threaten vehicles with destructive high-speed impacts. On the earth, the atmosphere serves as a natural shield against many of these threats. But in space, astronauts and equipment need other forms of protection.