The observable Universe is a 92-billion-light-year sphere—a place so big that it's impossible to imagine its dimensions. But what if the Universe were as small as a scale model train? Then the Horsehead Nebula would look something like the above.
I came across this Imgur post and I thought it would be fun to try to make new and better ones. So I searched for suitable images that would look good after processing.
The technique is simple: open the original image as a base layer. Duplicate the layer and make it out of focus with the Gaussian blur filter. Then add a mask to that layer and use a brush to selectively mask the parts of the image that you would like to keep in focus so it looks as if you were taking a macro photo of a tiny model of the Universe.
Update: Reader Egils made a couple with the Lens Blur effect. Even better!
Here are my results:
It's a fun game. Some are better than others, but I would love to see your examples in the comments.