The solar chromosphere and corona
The chromosphere is a rarefied layer above the photosphere, ≈ 2000–3000 km thick; it is visible only as a red rim in a total solar eclipse (the hydrogen Hα line, 656.3 nm) or through a special Hα filter. Spicules – jets of gas shooting upward – rise from it. Prominences are clouds of cooler, denser gas held by magnetic fields, up to hundreds of thousands of km high. The corona is the Sun’s outer atmosphere, stretching several solar radii; its temperature is 1–3 million K but its density is very low, so it is faint: it can be seen at a total eclipse or with a coronagraph. Why the corona is so hot is not completely settled (magnetic reconnection and waves play a part). From the corona a stream of charged particles – the solar wind – flows out at ≈ 300–800 km/s and reaches the Earth in ≈ 3–4 days. The Parker Solar Probe, launched in 2018, entered the corona in 2021 and in late 2024 came within ≈ 6 million km of the Sun.
Task: make a strip diagram of the Sun’s layers (core, radiative zone, convective zone, photosphere, chromosphere, corona), with the temperature and one feature for each.