Calcium K Filters

The Calcium K (CaK) spectral emission line occurs at the violet end of the visible solar spectrum with the somewhat short wavelength of 393.4 nm. It indicates strong magnetic activity in the chromosphere and is associated with the chromospheric network. A CaK filter isolates the layer of the Sun that is below and slightly cooler than that observed at the Hydrogen-alpha wavelength of 656.3 nm.