The Celestial Cascade

When the Great Cataclysm shook the world, it scattered power across the sky like fallout. This power, which would later be known as Éla, hangs like an electrical current in atmospheric 'rivers' -- and once every few years, that current is visible.
When the circumstances are just right, the Éla in the sky reacts to increased solar energy and sparks, causing an intense light show known as the Celestial Cascade. This event is celebrated as a holiday by many cultures across Neria -- for some, it is a sign of a higher power's glorious presence. For others, it is a reminder of the great power the The Old Magi left untethered for better or worse. Some cultures view it as a message from the dead, while others see it as an ill omen calling for ritual and offerings to appease the powers above.
However the view of this event is seen, most cultures have some form of celebration to appease or celebrate this perceived symbolism. Even those who do not believe in the mythology surrounding the rivers will often look forward to the event in relation to the scientific advancements it has allowed.

In History

Documentation from during The Endless Night suggests that despite the blanket of darkness, the Celestial Cascade was a present phenomena during the fifteen years. Accounts describing it as the "life-giving lights" corroborate with mythology in what is now the country of Jordai on the easternmost arm of the Continent, confirming that the Cascade may have provided much needed visibility for its duration. Something within the Éla reflecting sunlight may have given life to allow far more crop growth, and may have been a large factor in the continued survival of society during the Night.

Manifestation

The Cascade appears first as what seems to be a handful of extra stars in the sky. Depending on where in the world an observer stands, these 'stars' may be barely visible against a backdrop of daylight. If the sky is overcast, these stars may not be visible.
Over the course of an hour more Éla will begin to react, lighting up in waves like the centers of countless galaxies in a scattered show of bright purple. If the sky is overcast the Cascade will be visible like constant waves of slow-rolling sheet lightning within the clouds, and by this point the reaction is bright enough to be visible in broad daylight.
Those closest beneath the waves have reported a 'buzzing' feeling in their fingertips or a chill in their spine for the duration of the event. Those closer to Tel Padria, the source of the Éla rivers, report a variety of symptoms from full-body tremors, to nausea and fatigue, to increased energy and flights of ideas. There are scattered reports of similar symptoms in locations where the Cascade does not occur, but these are scattered and mild so correlations to the event may be coincidental in these cases.

Localization

The Cascade is present across the world, localised in wide strips of air known as the Éla rivers, where the Éla scattered in the atmosphere by The Great Cataclysm is most concentrated. Scholars cite this event to be the first piece of evidence that led to the discovery and confirmation of the Rivers, and have given a visual map of where these rivers are spread. This has allowed cross-study with the concentration of Magi across the world, further confirming that they are most densely populated in areas beneath these rivers.
In most locations, multiple waves of the Cascade can be seen as the Rivers are close enough together in the atmosphere. The only exception to this is in the central territories of the Eastern Island, where a large gap between the Rivers is wide enough that parts of the area do not experience the phenomena.

The Celestial Cascade

The Celestial Cascade, seen through clouds

Frequency
Tri-annually
Time of Year
Early Spring

Type

Metaphysical, Supernatural

The Celestial Cascade as seen in bright daylight

The Celestial Cascade seen at night

A second line of the Cascade can be seen on the horizon.