A Chromosphere

The Sun’s chromosphere is usually optically thin at most wavelengths, allowing an unobstructed view of the photosphere. During a total solar eclipse, the Moon briefly blocks the photosphere's light, revealing the chromosphere's red glow, primarily from Hα emission. The Hα line's significant optical depth enables the study of the chromosphere. Large-scale structures, such as supergranulations, and smaller irregularities like A Spicule, can be observed and analyzed through filtered photographs that isolate specific spectral lines. Similar to granules in the photosphere, supergranules exhibit upward motion at their centers and downward motion at their edges, detectable through Doppler shifts of spectral lines.

During the brief moments just before and after totality when the chromosphere becomes visible, a thin sliver of light creates a curved slit effect. Using a prism or grating to analyze different wavelengths reveals a flash spectrum, showcasing curved emission lines. This phenomenon occurs as the Moon covers the photosphere but not the chromosphere. The spectrum displays emission lines because there is no strong continuum for absorption. Analysis of chromospheric spectra indicates a higher temperature compared to the photosphere. Despite the chromosphere's higher temperature, its optical thinness minimally contributes to the overall radiation observed from the Sun. The challenge remains to explain the temperature rise with increasing distance from the Sun's center.