Astral Shower

The glowberry is a fruit that normally tastes awful and provides little sustinence, most refer to glowberries as <name>. The Lumis trees which grow only in the rarest of enchanted forests and known for their vibrant silver leaves that glimmer in the moonlight are the producers of the glowberries. The glowberry only glows during a special event, the Astral Shower.
The star metal that is left from the Astral Shower is collected by the Elves and used to create their most sacred works. This could be tools, arms and armor, and ornate crafts.
The Astral Shower is a phenomenon that occurs once every few decades when Seiderheim aligns with the path of the comet <name>. When the comet passes the world it rains down meteors and showers it in an astral dust. As the dust settles it's composition reacts with the glowberries making them light up the forest in an absolutely enchanting manner. The people love the Astral Shower since it brings light to these berries, making them delicious and useful.
When the berries start to glow it lasts for about a week before they start to fall from the trees and sprout into new ones, it is at this time they must be harvested but not too many for new trees must be grown to keep the generations of forest alive.
As the fruit begins to glow it gains unusual properties, alchemists mix the famous "Elixir of Illumination" when the berry is glowing. The potion glows mysteriously and when imbibed enhaces magical abilities as if some astral power is bringing pristine clarity to their thoughts allowing them to hyperfocus on the spell they're casting. There are several other potions that can also be crafted during the time that the glowberry is vibrant. Some Elves even make wine from the berry in its glowing state.