Bonjour 4ndy,
I would do is create one strong light, white, for the sun. This light has specular and raytraced shadows.
But I would also add a blue backlight. This light comes from the Earth, it is the light that is reflected on the atmosphere and oceans. This light does not have specular and have wide shadow maps. I recommend that you use several distant lights instead of just one. Also, you can use, instead of light sources, planes that will emit Final Gathering, for a more uniform light but longer render times.
If you don't have any Earth in your scene, perhaps you have nebulas or gas cloud that could send colored light?
Hope this helps
Salutations - Cheers
Bernard Lebel