Definition
A stream of electrons emitted from the negative electrode (the cathode) of a vacuum tube when a high voltage is applied between the cathode and a positive electrode (the anode). The electrons travel through the vacuum and can be focused, deflected, and used to produce a visible image when they strike a phosphor-coated surface.
Plain English
A flow of tiny negatively charged particles shot out from the negative end of a sealed glass tube. When these particles hit a special coating on the inside of the tube, they make it glow, which is how older screens produced a picture.
Context Anchor
Seen in basic aircraft electronics, older radar displays, and cathode-ray tube display discussions.
Derivation
From the Greek 'kathodos,' meaning 'a way down' or 'descent.' Early experimenters saw the rays appearing to come 'down' from the negative electrode into the tube, so they named the source the cathode and the rays after it.
Why Pilots Care
Many legacy aircraft instruments, weather radar displays, and engine monitors use cathode-ray tubes. Understanding what cathode rays are helps when troubleshooting display problems or reading maintenance documentation on older avionics.
Grounding Statement
Picture an older display tube: electrons leave one end of the tube, shoot across the empty space inside, and light up a spot on the screen.
Intuition Check
Cathode rays are not rays of light. They are moving electrons that can create light when they hit the screen.
Example Sentence 1
The old radar scope used cathode rays striking a phosphor screen to paint the weather returns the pilot was watching.
Example Sentence 2
Maintenance crews checked cathode ray tubes for brightness before flight testing the instrument panel.