Green Line (557.7 nm)
Definition
The specific green wavelength emitted by atomic oxygen — the aurora's signature color.
In plain language
The aurora's famous green is one exact shade: light at 557.7 nanometers from single oxygen atoms roughly 60–120 miles up. It baffled scientists for decades because it cannot be produced in ordinary lab air.
The science
The 557.7 nm emission arises from the O(¹S → ¹D) forbidden transition (~0.7 s lifetime), collisionally quenched below ~100 km. Its laboratory identification in 1925 resolved a 57-year spectroscopic mystery.
Why it matters for aurora viewing
Green marks the aurora's standard altitude and your eye's peak sensitivity — the first color you'll see and the benchmark of every display.
See this in action on tonight's data.