As seen in the picture, the planet is ‘cut’ in half with a different light.
I don’t think it has anything to do with the directional light in the scene but with the shader on the planet. I’m not yet getting into shaders so I don’t really understand it yet.
How do you want us to know? we don’t know how you want it to look, and we don’t know what shader you’re using.
Explain what’s wrong with the current look, how you would like it to look like, and share your shader code so that we can find the source of the problem.