By Corina Fiore Updated Mar 24, 2022
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The chromosphere is a thin outer layer of the Sun, positioned just above the photosphere—the layer we see from Earth. Its distinct reddish hue comes from the hydrogen alpha emission line it emits. This subtle glow is usually only visible during a total solar eclipse, but modern telescopes can isolate chromospheric light by filtering out all other wavelengths.
The red coloration is produced by hydrogen alpha emission. Although it is much fainter than the photosphere’s brilliance, the chromosphere’s spectral signature can be captured with specialized filters.
The chromosphere spans roughly 2,000–3,000 km (1,243–1,864 mi) in thickness. Its temperature ranges from about 6,000 °C (10,800 °F) near the base to 50,000 °C (90,000 °F) at the top, increasing with altitude. Scientists attribute this rise to magneto‑hydrodynamic waves: oscillations in the Sun’s magnetic field that transfer energy upward.
Supergranules are large bright and dark regions within the chromosphere, far larger than photospheric granules. The Sun’s magnetic field clusters along these cells, forming a complex web of field lines. Where these lines converge and become tangled, the temperature drops, creating darker patches.
Filaments are elongated, dense gas structures that appear darker because they emit less red light and are cooler than their surroundings. When these filaments are observed at the solar limb, they are called prominences.
Spicules are slender jets of plasma rising from the chromosphere. With diameters of about 480 km (300 mi) and heights exceeding 7,000 km (4,300 mi), they streak upward at roughly 30 km/s. Though short‑lived—lasting around 10 minutes—over 100,000 spicules can be present simultaneously, giving the chromosphere a jagged appearance.
