T72B 
this looks great for your first picture!
for some easy lighting and shadow effects add a new layer and set it to ‘multiply’. then bucket fill it with a medium grey red/orange. this will make everything look like its in shadow. then on the same layer you can use a light orange or yellow to show the highlights around the sun, and were the light shows on the edges.
for much brighter lighting add a new layer on top of the multiply. set this one to ‘overlay’, and using a large airbrush with a light yellow or orange, color over the sun to really make it shine
this is a pretty basic way to do it, but it can be a good starting point. as far as i am aware every drawing program above paint should have these layer blending modes