well the algorithm would be complicated, but i guess it is based on magnetic attraction, since thats what happens on the sun...
for the glow, just use a glow sprite, and put it in the sun axis, and facing the camera, with the function
ent_create("glow.png", sun.x, NULL);
your.pan=camera.pan
your.tilt=-camera.tilt
and so on
OF course there is better and more quality aproaches using Post processing glow etc...