Chromosphere

Chromosphere is a layer of the Sun's atmosphere located above the photosphere and below the corona. It extends roughly 2,000 to 3,000 kilometers above the visible surface. Temperatures increase with height, rising from about 4,000 kelvin in the lower chromosphere to around 8,000 kelvin in the upper chromosphere.

Visible primarily during solar eclipses or with narrowband filters that isolate the hydrogen-alpha line, the chromosphere appears as a pale red glow. Its structure is highly dynamic and features a range of phenomena, including spicules—thin, jet-like upwellings of gas—filaments and prominences near the solar limb, and bright regions known as plages associated with magnetic activity. The layer also emits strong lines from hydrogen (H-alpha) and ionized calcium (Ca II H and K).

The chromosphere is not uniform. It contains rapidly moving gas, shocks, and complex magnetic fields that shape its appearance and drive energy transport toward the outer atmosphere. Its temperature rise contrasts with the cooler photosphere below, reflecting the existence of heating processes that counter radiative losses.

Role in the solar atmosphere: The chromosphere forms part of the transition from the largely neutral photosphere to the highly ionized corona. While the exact heating mechanisms are still researched, magnetic fields and waves from the convection zone are considered important contributors to its energy budget and dynamics.