Building the earth

According to the Bible, in the beginning, the earth was unformed and void. But in Unity, it starts as an untextured sphere. 3D objects in Unity, such as spheres, cubes, or arbitrarily shaped meshes, are rendered by default using an untextured default material.

Materials define the details of how the surface of an object should look, usually using texture images. A texture is an image that is mapped onto the surface of an object as if it were painted or was a wallpaper. This is referred to as the Albedo texture or surface reflection. Advanced materials can use other textures to simulate additional surface detail, bumps, rust, metals, and other physical characteristics.

Suppose a sphere had a surface texture like this:

The texture unwrapped from the sphere and flattened into a 2D image is called an equirectangular projection, as shown in the following figure, much like you would find in the maps of the world (see https://en.wikipedia.org/wiki/Equirectangular_projection). This...