Physical Sun and Sky:
An easier way to get an interesting looking sun and sky for your objects is with the physical sun and sky.
To do this make sure your render settings are on Mental ray. If it isn’t, then click on the slate board looking icon. In these settings you will see a Quality tab, change the quality preset to production. Next we go to the Indirect Lighting tab and click on the “Create” Button next to Physical Sun and Sky. This will create the sun in your Maya scene. Add a couple of objects, a NURBS plane and sphere. You will notice a sky and sun which you can add objects and manipulate the intensity to get a very nice looking atmospheric effect.