Fun fact: They make the mirrors for these telescopes in Arizona, then somehow have to get that mirror up a Chilean mountain. Don't quote me on this, but I believe the way they get the mirror into shape is by rapidly rotating it. The centrifugal force makes a parobolic equi-potential surface on the liquid glass...you can see this by rapidly spinning a cup of water. Construction on the mirror started in 2008 despite construction on the telescope starting last year.