PixelRebirth
Like a real sun effect, which glows & gives a shiney effect
I'd suggest you look into dynamic lights first of all, to give you a feel of what Construct is generally capable of regarding lighting.
A glowing sun, well, that's usually done with a combination of effects and sprites. It depends on how you want it to look.
Something like the following
<img src="http://dl.dropbox.com/u/2306601/nightp_gt_1.png">
is simply done with sprites and the additive effect. Other useful effects for your purposes could be superBloom and Color Fusion.