The second stage of the image was completing the top half which involved adding the moon, stars and clouds. This was a bit easier than the first stage as I already had the photos and not a lot of editing was necessary.
For the stars I used an old photo I took on a clear night with a 15 second exposure time, which I then edited to increase the light levels and make the stars more visible.

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As for the moon, I took several photos through my telescope at home and got some crisp and clear photos without any cloud pollution. After looking at a selection in Photoshop I decided on one to use:

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I experimented with these two images and various other layers and filters until I had them arranged how I wanted them. I decided that i'd give the whole image a "blue theme" since the water was blue anyway and the moon could be a blue moon. So I added a cooling filter and changed the light levels for the moon to make it look as if it was brighter and giving off more light. Also, I gave the stars a very slight blue tint although it's barely noticable.

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Finally I started trying to get the lighting right to make it look like the sea was being illuminated by the moon.