How to make a realistic planet in Blender (2004)
Earth in Blender

This tutorial works also with earlier versions of Blender than 2.30, besides the fresnel effect that, in fact, in 2.23 I had to fake. To fake the fresnel I used two ways: the first, the faster for rendering, used a "blend" procedural texture; the second, slower for rendering but more effective, used a circular set of dupliverted lamps to light the "borders" of the planet.
Two old techniques

Here above you can see the effect of the two techniques. Anyway, because now Blender has a true fresnel effect, we don't need anymore to fake it.

The following is the technique I used for the planet in the image "Golden Planet", using Blender vers. 2.31a.

The set
The first thing to decide is: have we to do a whole planet or just a slice of it? For the Ovoships image (and animation) I opted for the slice (a "dome"), because there was no need for a whole sphere. The technique, anyway, works just the same, but with a slice we can easily use very big and detailed textures. So, let's start adding a big uv-sphere primitive to our scene...

The set

... and then erase the unnecessary vertices to have the dome. This way we keep the geometric centre of the object as if it were the whole sphere. This is useful for the next step.

The set

With SHIFT-D duplicate the dome two times, each time increasing the size of a bit (for this use the N key); for example, the starting dome will have size = 1.000, dome 2 will have size = 1.002 and dome 3 size = 1.004. The first dome will be the planet surface, the second one the clouds layer and the third the fresnel effect of the atmosphere.

The three layers

Then add a tube primitive to the scene and scale it to make it larger than higher (see the following image). I mapped the tube in uv mapping, on each face so to have a perfect ring, with this "gradient" texture:

The texture for the atmosphere effect

The atmosphere

This ring must be placed around the three domes; more details about the material at page 4.

The set

Here it is our completed set. I placed a spot with shadows as key-light, a "quad/sphere" lamp at the geometric center of the domes to fake the planet radiosity and an other lamp on a side, to have a light blue radiosity effect from space...

The planet surface material
Of course, a very important thing is the kind of textures we choose and the way we are going to use them. For the Golden Planet main color I used this texture (it's a faked Venus color map that you can easily find on the net):

The color map

But before the textures comes the general material setting for the planet surface:

The surface material

You can see that I used all the eight texture slots, and we are going to see all of them in detail. First, this is the setting for the color map ("colvenus"):

Color map setting

I applied the texture in uv mapping (a simple "from window" option from above), but actually orco mode would have worked too.
(Well, of course, if you are doing a whole planet you have to apply it in sphere mode...)

Color map applied

The color map applied. Then I loaded a grey scale version of the same texture both for the specularity and the diffuse channel ("specvenus" and "diffvenus"):

Specular and diffuse maps applied

And then also for the emit channel ("emitvenus"):

Emit map applied

At this point, because the texture has not defined continents, it's time to create someone. I used this slightly modified (the "rivers") Earth map and I created its alpha channel (the checkered background is the Gimp's one):

The mask map

Seems that in Blender the limit for tga with alpha channel is a 4000 dpi image; bigger targas with transparency don't show in the rendering, nor in the texture's preview window. But the image has to have an alpha channel of its own because, as you can see here, it must work as a "stencil":

Stencil map setting

This is the result ("maskoceani"); the stencil map works on the specularity and has a little bump effect too...

Stencil map applied

... and, as you can see in the below image (rendered with only the stencil channel active), the stencil map "splits" the seas from the lands.

Stencil map effect

At this point we add a procedural texture to the surface; this is just to display the "sphericity" of the planet. Choose a "blend-sphere" and set it this way:

The general blend setting

A general blend

Now it's time for an other procedural, stucci, to add a kind of "roughness" to the oceans surface:

The stucci setting

The ocean's specularity

Set the stucci's size as little as you can.
And now a last procedural for the oceans (damn!... No more texture slots...), a "blend-sphere" again:

The ocean's blend setting

The ocean's blend

Of course, all the textures we placed after the stencil map ("maskoceani") will affect only the oceans, that is the transparent areas of the stencil map.

Well, the planet surface is ready. Now let's go for the clouds!

The clouds material
As for the stencil map, I made a tileable 4k map with alpha channel of the clouds. Then I set the material:

The clouds material setting

The first texture channel work as a stencil for the transparency of the clouds; the others are for tweaking color, bumping, specularity, diffusion and a little emit:

The clouds1 material setting

The clouds2 material setting

The clouds3 material setting

The clouds4 material setting

I copied the oceans stucci from the surface material and pasted it into the clouds'one, to have a little more movement:

The clouds-stucci setting

And last, I copied and pasted also the last blend we used for the surface ("blendvenus"), to amalgamate the clouds layer to the surface's one:

The rendered clouds layer

The fresnel
The fresnel effect is really simple, and there is no need for textures of any kind:

The fresnel setting

The fresnel effect

The atmosphere halo
As I've already explained at page 1, the halo is a simple gradient image mapped with uv on a tube, to have a ring around the planet domes. This is the material:

The halo material setting

Two textures for the halo, the first for the color and the second for the transparency:

The halo color setting

The halo mask setting

The rendered atmosphere halo

At this point, we are done. By rendering all this together, we have our Golden Planet:

The completed Golden Planet

All this works perfectly with animations too; but if you are planning to make one, let me give you two advices.
Instead of the stucci procedural for the oceans and the clouds, use the "fixnoise.dll" plugin, it avoids the disturbing flickering of the pixels on the screen (at least if you enable the motion blur button...). If you are going to render a whole planet, don't worry about the atmosphere halo effect; in a real shot it wouldn't be visible at all from such a distance (as you can see in many NASA images of the Earth's far orbit).

That's all. See ya!