If you aren't sure what a spacewalk is, or why Tim Peake is going on one this afternoon, here's everything you need to know. Including the ways past ones have gone wrong. Read more at http://trib.al/Io1QIDC | Sky News

Historic footage from Apollo 9 shows the first full test of true spacewalk systems in Earth orbit. What may look unstable is normal in microgravity, as visor and checklist hardware float freely. This mission proved astronauts could work safely outside a spacecraft before going to the Moon. Follow @spaceeves #Apollo9 #Spacewalk #NASA #SpaceHistory | SpaceEve