Hi guys, here are some of the basic principles behind painting a glowing light source (the sun in this case), based on outdoor painting observation taken through to a studio painting. You'll notice some color difference between the video and the photo above - that's because I got a little setting wrong in the camera this time - sorry. (It was the ISO setting if you're wondering). Also, I fiddled around a little bit with this painting after I finished the video (couldn't resist) so this photo shows the sketch slightly more developed that where I finish in the video.
The Hudson River School of artists was a famous American group who were reknowned for using this type of backlighting effect in their work - well worth a look!