1: The starting image.

2: Ctrl-T then drag it down, giving it a slight element of depth.

3: Blurred the horizon with gaussian blur, did some contrast and brightness too.

4: Starting to build the sky.

5: Blurred the sky and turned up contrast & saturation.

6: Didnt like the sun in the middle, so merged 2 pieces together.

7: Rule of thirds (used in photography). I dont want the horizon in the middle.

8: Finished the horizon, flipped it horizontally.

9: Blurred the sky even more, and made it darker very gradually on the left hand side.

10: Red line indicates the line i will use to make cliffs.

11: With a black soft brush i carved out along the line. Note how there is 1 bit that shows the 'rock' thats vertical.

12. I grabbed the starting image, carved out a piece of it to resemble the vertical rock (i didnt use ctrl-t with this bit). Also added a lil mountain and a sun

13: Removed the right side of the canyon and started out shading everything along some lines. Look at the sun and imagine what areas get shade. Used a soft black brush on the shading part, and the dodge tool to highlight areas that the sun catches. Also blurred out the distant rocks.

14: Added some water.

15: Added a stream in the water and shaded the 'river'. also blurred out the 'sea / lake'.

16: Started with giving the background and left side some greenery. the start of the bottom green layer.

17: More shading, dodge tool and plants on the right foreground. Also added a water texture to make it more realistic.

18: Added plants using the Bob Ross brushset (i dont know if its still out there, i downloaded it ages ago). At this point i still wasnt happy with the plants.

19: Decided to add some flowers, found them on cgtextures.com and added them in the picture UNDER the shadow layer. by using an irregular brush like a plant brush as an eraser, i managed to blend in the plants nicely.

20: Added a planet by grabbing a Mars texture from planetpixelemporium.com. I selected a circle, then using Filter - Distort - Spherize twice and adding some shading on the dark side of it to give a 3d effect. Also added a hint of atmosphere to that planet using inner and outer glow.

21: Shaded the top right some more, added some stars, and a bigger flash using Filter - Render - Lens flare, and modifying it a bit.

22: Added some white/orangy clouds, made the bright stars a bit smaller, modified some minor stuff and added a border.

All finished :)

If you have questions feel free to ask, but do keep in mind that I can only give a general idea of what I did. These 22 pictures cover over 10 hours of work (my workflow isnt that fast). I hope you enjoyed this little walkthrough :)