way to get rid of sharp line in shader

Hi

I created a planet shader that uses emissive color on a unlit Shading Model.
I am using the dot product of a vecter with the pixel normal to fake light coming from a sun.
Is there a way to smooth out the transition between light emitting until no light ?
here is a picture as example whats going on.

ce1d00438db3b27a847e9402d08a6b18c5250d67.jpeg