Aurora
How auroral arcs, curtains and rays behave, how local probability differs from global Kp, and why cloud cover still matters.
What the aurora is
Aurora occurs when energetic particles associated with the solar wind interact with Earth’s upper atmosphere along magnetic-field geometry. To an observer, the visual result can range from a faint grey-green arc to rapidly changing curtains and rays. The event is spatially extended, unlike a single aircraft or satellite point, and can cover a substantial part of the sky.
Why Kp is not a local forecast
The planetary Kp index summarizes geomagnetic disturbance on a global scale. It is useful context, but one number cannot tell you whether aurora is over a specific town or visible through local cloud. Sky Event Radar therefore also samples NOAA’s current OVATION auroral grid for a near-current sighting. Local probability is a more direct piece of context, although it still does not guarantee visual visibility.
Cloud can imitate or hide aurora
Low clouds can glow green, orange or red from artificial lighting and can form broad patches that resemble aurora in photographs. Conversely, genuine aurora can be completely hidden by cloud. This is why local cloud cover and visibility are included in the same evidence report as geomagnetic data.
Camera versus eye
Modern phone cameras can reveal color that is difficult to see with dark-adapted human vision. A faint auroral arc may appear grey to the eye and distinctly green in a long exposure. The reverse problem also exists: automatic white balance and aggressive processing can make ordinary cloud glow more dramatic. Preserve the original image if later verification matters.
Historical aurora requires historical evidence
A current OVATION map must not be used to explain a sighting from last week. For older reports, the local live layer becomes not applicable. Historical geomagnetic archives can be consulted separately, but the site does not substitute present conditions for past evidence.
Common confusions: what it is most often confused with
Illuminated cloud
Cloud follows lower-atmosphere structure and local light sources; weather context is essential.
Airglow
Usually fainter and more uniform, often revealed mainly in long exposures.
Light pollution
Fixed relationship to cities/horizon and cloud base is a clue.
Rocket plume
Often a coherent expanding structure tied to launch timing and twilight.
Questions observers actually ask
Can aurora appear red?
Yes. Emission altitude and atmospheric species can produce red as well as green and other colors.
Why does my phone see more than I do?
Longer exposure and sensor sensitivity can accumulate faint color that the eye perceives mostly as grey.
Does high Kp guarantee aurora where I live?
No. Latitude, local oval position, darkness, weather and viewing direction all matter.
Test this against the actual place and time.
Weather, aircraft, fireball, aurora and launch context can strengthen or weaken this category for a real sighting.