Ultraviolet
Here is a portrait of the Sun captured through a specialized solar telescope that transmits light at the calcium K-line – a narrow slice of the spectrum in the near UV. This wavelength shows the details of the low chromosphere – a crackling texture, here undisturbed by active regions or sunspots. This tranquillity is the signature of solar minimum. In 2019 the Sun showed no sunspots on 281 days.
Alan Friedman