Look in my pictures in my profile. I did a quilt called Stars Ablazin where I quilted a starburst pattern radiating out from the center of the star to the tips. I think something like this would work very well for your sun. I made a template for marking so I could keep my curves uniform. I also used red thread so it would show up better. You might consider a bright yellow or orange yellow for yours. Because of the way the star was peiced there were areas where VERY large numbers of fabric layers were coming together - I just dealt with those by stab stitching through when needed. Good luck and let us know how it came out.
Edited because my mind reversed the sun color while I was typing lol.
How about a big swirl in the center and straight lines (on both the red and white) out from the center there reflecting the sunburst? I'm not sure what colors I would use, it would be more than one though.
If anyone has time to look at my profile, I have a wall quilt photo posted that I am stuck on. I don't know what to do with the quilting on the sunburst in the middle. I am planning on using blue/gray thread to quilt the border and the area surrounding the sun. The fabric has trains on it - so I was going for a kind of geometric train-inspired theme for that quilting.
But for the sunburst I am clueless. I'm not sure if I want to use red and yellow thread or stick with the blue thread. The sun is also only 8 inches wide, so there is a lot of fabric in there - and I am a handquilter and not sure how I will handle all the layers.