Black sphere within skybox sphere forms when I try using a giant sphere to create a skybox in threejs

Question

I'm trying to make a spherical skybox since I think that would best fit the space scene I'm making. I'm running across two issues:

1. I can get the skybox to work, but for some reason a sphere within my giant sphere I've made appears. I don't think its a real Object3D sphere, I have the feeling its a graphical glitch of some sort.

2. If I make the sphere too big (Like 1800 for the radius) it just disappears and stops working. If I set it's side to THREE.DoubleSide, I can zoom out of the scene and still see its outer side of the sphere, but inside, regardless of DoubleSide or BackSide, its invisible when 1800 or bigger

let skyboxGeom = new SphereGeometry(900, 128, 128)
let skyboxMat = new THREE.MeshPhongMaterial({map: spaceTexture});
skyboxMat.side = THREE.BackSide
let skybox = new THREE.Mesh(skyboxGeom, skyboxMat);
skybox.position.set(0,0,0)
mainScene.add(skybox)

Here is a picture of what it looks like:

The colorful ball is correct, the inner black sphere is what appears incorrectly. If I zoom in enough to the scene, the black ball shrinks and gets smaller and smaller until it disappears entirely, but I would have to zoom way too far into my scene that none of my things would show if I tried to do this to make the black ball go away

If it helps, I am using a PerspectiveCamera, and am exploring the scene using OrbitControls