How to build a telescope at high altitude
2 October 2011 Last updated at 10:34 BST
Astronomers in Chile have been building the world's most powerful telescope high up in the Atacama desert.
The Alma (Atacama Large Millimeter/submillimeter Array) telescope facility involves the construction of 66 giant antennas on top of a 5,000m-high plateau.
At these heights, people can very easily suffer from altitude sickness.
Pallab Ghosh has been to the site to ask medical staff there how they deal with the problem.