3d printed shoes

The next revolution is on it's way. When anybody can make their own shoes, clothes and accessories or sell them to those that can't or don't want to, things will become interesting.

It has started with 3d printed shoes.

Image source:
http://www.infoniac.com/offbeat-news/dutch-artist-creates-3d-printed-shoes.html

why is the sky not violet

After reading this xkcd strip I wondered the same thing. Off to my favourite activity: seach the internet for answers.

The sky is blue because:
1) Shorter wavelengths are scattered more (Rayleigh scattering) than longer ones and therefore the radiation that reaches use is shifted to the blue-violet part of the visible spectrum.
2) But our eyes see better towards the middle of the visible spectrum and can't see the violet as well as the blue.
And therefore the sky looks blue to us humans.

Source:
http://www.msnbc.msn.com/id/8631798/
http://apollo.lsc.vsc.edu/classes/met130/notes/chapter19/rayleigh.html