A heated layer above a photosphere can have an outward temperature increase. Strong lines formed there may show emission where an outward-cooling photosphere would produce absorption. The energy maintaining the temperature inversion is additional atmospheric heating; the exact height and transfer regime vary between stars.
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The chromosphere is a layer of the Sun's atmosphere that lies above the photosphere and beneath the corona. Its name, derived from the Greek words for "color sphere," reflects its reddish appearance during solar eclipses when it becomes visible. The chromosphere is characterized by a temperature range of about 4,500 to 20,000 Kelvin, which allows it to emit light primarily in the hydrogen alpha spectral line, giving it a distinct reddish hue.