One of the goals we have is giving the player the feeling of traveling in the depths of space. Because that feeling of being in outer space is one of the best experiences we can have in a space-themed game. This is how we do it.
1. To build the backgrounds, we created a shader on Unity, that has different layer (images or textures) which overlap each other but they have different speed levels.
The material allows us to custom any layer speed whichever we want to reach our desired effect. For the time being, we are working with 4 layers: the main background and 3 layers over it which give the illusion of depth.
2. Since each layer will be moving at a different speed, we created a function that is set up to do exactly the same so we didn't need to repeat the process 4 times.
3. Here is how it looks in the inspector
4. And finally the result in Unity.