What a gorgeous July morning in the south of the UK. Looking up, I'm struck by both the wonder of the universe and man's impact on our corner of it. The blue colour is caused by the fact that blue light (which has a shorter wavelength than red) is scattered more readily by our atmosphere. At sunset, we see the opposite because we're looking at the sun in a straight line and all the blue has been scattered in other directions.
In the photo, you can see the vapour trails left by commercial airliners passing silently overhead – amazing to think that this is a modern phenomenon, something our ancestors wouldn't have experienced. Unless aliens really did land in the distant past!
And Mr Blue Sky is the most famous track by my favourite band – the Electric Light Orchestra. No better way to get into the summer mood!