Using Bump, Specular, & Alpha Mask Image Map Textures (Earth & Moon)
by Geno Ruffalo

In Blender each Material can have up to 8 Textures linked to them. This tutorial will
cover how to use specialized images in these texture channels to create realistic
Earth and Moon Materials. The final image will be composed of 4 types of Image Maps:
Color, Bump, Specularity, and Alpha Masking.

The first Image that is usually applied will be the main Surface, or a picture
of the Earth itself. If you have not done so already, create a new Material (F5)
and create a new Texture (F6).Throughout this tutorial the pictures below will be
the settings and the links will be to the texture images themselves. So click on
the image below to load the Image, save it to your harddrive, and assign it to the
new Texture.

The next image that we will apply will be the Bump Map. Bump Maps are usually
greyscale images where the light and dark areas raise and lower the texture to
give the over material a deeper textured appearance. To use a Bump Map create a new
Texture for the Material, load the image, and activate the 'nor' button while turning
off the 'col' option. We don't want the Bump Map to contribute any color to the
overall Material. The 'Nor' slider button can be adjusted to increase the effect.
To reverse the highs and lows click the 'nor' button so it is yellow in color, as in the
example below.

The next step is to apply a Specularity Image Map. The Earth's Oceans
will relect more light than the land masses will. I took the image of the
Earth, and turned it into a Halftone image. The black land masses will now
block out the shine from the sun and give us a more realistic overall appearance.
Load the image and push in the 'spec' button while turning off the 'col' button
as we did with the Bump Map. In the Material Buttons set the 'Spec' slider
button down to zero.

If we want to add some semi-transparent clouds to the Earth we can
create a new sphere at the exact same location as the Earth but scale it
just a little bigger. All we need is a new Material with one new image that
we will set up as an Alpha Channel Mask. Load the image in the Texture and push
in the 'CalcAlpha' and 'UseAlpha' buttons. In the Material buttons push in the
'Alpha' and 'sub' button. Set the 'Alpha' slider button as shown and push in the
'Ztransp' button. Set the Materials main color to a bright white. Since the cloud
Image is greyscale we can add to the texture by also using it as our Bump Map by
clicking the 'nor' button.

The Moon only needs 2 Image Textures, a Color Image Map and a Bump Map.
The Image below is the Main Image and clicking ot it will take you to the
Bump Map. Set it up the same way as the you did for the first 2 steps for the Earth.
Since there is no Specularity Map make sure to adjust the 'Spec' slider button
to your liking.

These techniques can be applied to all kinds of Meshes and Surfaces.
The best way to test them out is to create a basic Sphere and Plane, add
some lighting, and load each type of map individually and play around with
the different settings. If you were to add animation to our Earth, make the
outer sphere that we used for the clouds and rotate it just a little slower
that the Earth's Sphere. This will give your world a true to life look.