Definition
A colorless, odorless, non-flammable gas that is the second-lightest element. It is present in very small amounts in Earth's atmosphere and is best known in aviation as the lifting gas used in lighter-than-air craft such as blimps and weather balloons.
Plain English
A very light, safe gas that floats in air. It is what fills blimps and many weather balloons so they can rise.
Context Anchor
Seen in discussions of what the atmosphere is made of, especially when listing the gases in air.
Derivation
From the Greek 'helios' meaning 'sun.' Helium was first detected in sunlight before it was found on Earth, which is why it carries the name of the sun.
Why Pilots Care
Helium is a small but real component of the atmosphere pilots fly through, and it is the standard lifting gas for blimps and weather balloons. Unlike hydrogen, it does not burn, which is why it replaced hydrogen in airships.
Intuition Check
Do not think of helium only as “balloon gas.” In this chapter, helium is being named as one of the small-amount gases naturally present in the atmosphere.
Example Sentence 1
Along with nitrogen and oxygen, the atmosphere contains trace amounts of gases such as argon and helium.
Example Sentence 2
At high altitudes the relative proportion of helium remains nearly constant even as overall air density decreases.