Why Sodium D-line?
Sodium will give high resolution sunspot detail, plague, granulation, and possibly the super-granulation depending on resolution and seeing of the observer.
Sodium can also show flare footprints, also known as flare kernels.
That is that a flare will begin and emit light in Sodium at the 2 ends first, before erupting in white light.
The line is brighter than both Calcium and even Hydrogen Alpha. So it's going to be very easy for observers to see and the exposures will be very short.
We'll be doing D2 line on 5890
Sodium D line Quarks will all be 0.5 or narrower.