How do you create a sun/moon/lightning/raining effect in Unity 2D?

I have been playing with Unity lighting and cannot figure out how to create a circular shape lighting like the sun/moon in Unity 2D! A great example would be Alto's Adventure: https://www.youtube.com/watch?v=Wk5JupHelAg

Also, I couldn't find a any example or tutorial to create a lightning/raining effect a great example would be Ori and the Blind Forest: https://www.youtube.com/watch?v=cklw-Yu3moE