the post processing magic
1. Adjusted the colour temperature. The raw file had a very brown tone.
2. Added noise reduction (remember: ISO 6400!)
3. fiddled with exposure to get the right darkness of the sky
4. Increased the colour saturation of the blue channel.
5. Removed the vignetting (result of shooting wide open)
6. Applied a curves adjustment layer in Photoshop to bring out the stars a bit more (ground and stairs masked out)
7. some dodge and burn to bring out the milky way a bit more.
8. Done.