Shockingly enough, the sky box is procedurally generated! The sun was a random texture I found in the toolbox and same for stars. The sun and the stars are BillboardGUI’s, the skybox I have is completely black.
In case you want to replicate the sun flare effect I’d recommend you to search in the toolbox for textures or “flare effect” models and manipulate how BillboardGUI’s can move parallel and along with the screen given the offset variables given to them.
Hope this answers your questions, thanks for commenting! 