apusäikeitä

Apusäikeitä, often translated as "star threads" or "celestial threads," is a Finnish term referring to ephemeral, colorful, and wispy phenomena observed in the upper atmosphere. These visual displays are typically seen shortly after sunset or before sunrise, when the sun is below the horizon but its rays still illuminate the very highest layers of the atmosphere. Apusäikeitä are characterized by their delicate, thread-like appearance and often exhibit a range of pastel colors, including pink, orange, and violet.

The scientific explanation for apusäikeitä involves the scattering of sunlight by very small particles and ice crystals suspended at extremely high altitudes, typically in the mesosphere. These particles are much smaller than those responsible for more common atmospheric optical phenomena like rainbows or halos. The specific color and appearance of apusäikeitä depend on the size distribution of these particles and the angle at which sunlight strikes them. While visually similar to noctilucent clouds, apusäikeitä are generally considered to be a distinct phenomenon, often appearing more diffuse and less structured. Observing apusäikeitä requires specific atmospheric conditions and a clear view of the twilight sky, making them a relatively rare and enchanting sight for those who witness them.