Definition
A soft, silvery-white metallic chemical element (symbol Rb, atomic number 37) belonging to the alkali metal group. In aviation, rubidium is best known for its use in rubidium atomic frequency standards, which provide highly stable timing references used in navigation systems, GPS receivers, and avionics test equipment.
Plain English
A metal element used to make extremely accurate clocks. These clocks keep such precise time that they are used inside navigation and positioning equipment where even tiny timing errors would cause large errors in position.
Context Anchor
Seen in avionics, navigation equipment, and maintenance documents that discuss very accurate timing sources.
Derivation
From the Latin rubidus, meaning 'deep red,' because the element produces bright red lines when its light is passed through a prism. The name was given when the element was discovered in 1861. Knowing this helps explain why the metal itself is unrelated to anything red in appearance — the name comes from how it shows up in laboratory tests, not from how it looks.
Why Pilots Care
GPS accuracy depends on extremely precise timing. Rubidium clocks inside satellites and ground reference stations keep that timing stable, which is what allows a GPS receiver to fix position within a few meters.
Example Sentence 1
The GPS satellite carries rubidium clocks to keep its timing signal accurate to within billionths of a second.
Example Sentence 2
During preflight, the technician verified the rubidium frequency standard was locked and stable before engine start.