Silhouetted Sunset mountains in GIMP

This is a nice, basic way of silhouetting an image, and giving it an artificial sky, and glow from the sun.

You will need some basic GIMP skills, but (I find that) most of it is self explanatory.

Step 1 Take your picture.

First you need a picture of some mountains/ hills/ something that looks nice silhouetted.
This is my picture, of the Christchurch port hills.

Load it into the GIMP (File>>Open) and click Colo(u)rs>>Threshold. Slide the slider until you get a nice silhouette (This may take some tinkering!) my final silhouette is the second picture.

OPTIONAL:
If your picture is a panorama (like mine), not a nice 4:3 ratio, I changed the canvas size (Image>>Canvas size) to be the right size, then click Layer>>Layer to image size.
If you have a widescreen, you may not want to do this..