Why Last Week's Total Solar Eclipse Turned the Sun's Corona Gold

Last week's total solar eclipse produced more than a dramatic sky show: in Spain, it turned the Sun's faint outer atmosphere, the corona, a striking gold instead of its usual white or silvery color. During totality, the Moon completely covers the Sun's bright disk, making the extremely hot corona visible to observers on the ground. While many eclipse watchers along the path saw the familiar pearly hue, those in Spain saw something different.

The unusual color came down to geometry. In Spain, totality occurred while the Sun was already low near the horizon. Light traveling from a low Sun has to pass through a much thicker layer of Earth's atmosphere before reaching an observer, and that longer path scatters away more of the shorter, blue wavelengths of light -- the same effect that turns sunsets orange and red. With more blue removed, the remaining warm tones became far more visible around the corona.

A second factor added to the effect. Smoke from nearby forest fires was unusually heavy in the air that day, acting as an extra atmospheric filter. The smoke particles scattered even more of the remaining blue light, intensifying the golden tones around the eclipsed Sun.

The widely shared image of the golden corona was captured from Benavente, Spain, using high dynamic range (HDR) imaging, a technique that combines multiple exposures at different brightness levels so both very bright and very faint details can be preserved in a single photograph.

Not everything around the Sun turned gold: a large solar prominence -- a structure of glowing plasma extending outward from the Sun's surface, shaped by its magnetic fields -- remained visible along the Sun's left edge, its original bright pink color surviving because it emitted light strongly associated with hydrogen, a wavelength the atmospheric filtering did not remove.