Here it is again, the regular Sunday afternoon feature of this blog: a free background image. It's yours, for free. And you can use it wherever and however you like. Use it at home, at work, at school, at church. Use it on the farm. Use it in your particle accelerator(assuming, of course, that you have a particle accelerator...)
I only ask that 1) you share it freely and 2) that you tell others that you found it here.