Blue Flash

For only a fraction of a second, just as the Sun disappears below the horizon, Earth's atmosphere can reveal one of its rarest optical phenomena—the Blue Flash. Even more elusive than the better-known Green Flash, it occurs only under exceptional atmospheric conditions, making it a prize for both astronomers and seasoned observers alike.

As sunlight passes through the atmosphere near the horizon, it is bent and dispersed much like light passing through a prism. Longer wavelengths such as red and orange are refracted differently from shorter blue wavelengths. Normally, the atmosphere scatters blue light before it can reach the observer, leaving only the fleeting Green Flash visible. Under exceptionally clear and stable conditions, however, enough blue light survives to produce the extraordinarily rare Blue Flash captured in this image.

On this particular evening, the atmosphere above Maunakea was remarkably steady, with astronomical seeing measured at approximately 0.3 arcseconds—a level of stability achieved only on the finest observing nights. That same calm atmosphere which allows the world's largest telescopes to produce exceptionally sharp observations also created the perfect conditions for this fleeting flash of blue to appear. Lasting less than a second, it is a beautiful reminder that Earth's atmosphere is not merely something we look through, but a dynamic optical instrument in its own right.