WebGL Simple Lighting on the Earth
Swipe to Spin the Earth
Take a look at perhaps the simplest lighting shaders available. Vertex Y coordinates provide the amount of highlight. Vertex X coordinates provide the amount of alpha. Low alpha values on a black background with black WebGL clear color look like shadow.
Example of simple lighting on the earth with WebGL
NASA created the original Earth map. Seven Thunder Software modified the map with Photoshop. Read a brief tutorial which explains how to apply lighting for this example.