Earth's largest radio telescope is growing more powerful by the day on Llano de Chajnantor, a plateau high above Chile's Atacama desert, where visitors often feel like they're planting the first human footprints on the red crust of Mars. The 16,400-foot altitude, thin air and mercurial climate here can be unbearable. (Winds reach 62 mph and temperatures drop to 10 below zero.) But for astronomers, it's paradise.

The lack of humidity, low interference from other radio signals and closeness to the upper atmosphere make this the perfect spot for the $1.5 billion Atacama Large Millimeter/submillimeter Array, or ALMA, which is to be completed in March. So far, 43 of the 66 radio antennas have been set up. Linked as a single giant telescope, they pick up wavelengths of light longer than anything visible to the human eye, and combine the signals in a process called interferometry, which gives ALMA a diameter of 9.9 miles. The result is unprecedented resolution and sensitivity -- fully assembled, its vision will be up to 10 times sharper than NASA's Hubble Space Telescope.

More than 900 teams of astronomers competed last year to be among the first to use the array, and scientists are already taking turns at the joysticks. They're looking for clues about the dawn of the cosmos -- from the coldest gases and dust where galaxies are formed and stars are born, to the energy produced by the Big Bang. So-called birthing clouds of cold gases and debris can look like ink stains with other telescopes, but ALMA can show their structures. ALMA -- jointly funded and managed by the United States, Canada, the European Union, Japan and Taiwan -- also reaches farther beyond Earth's nitrogen-blue skies than any other radio telescope and has already captured images different from anything seen before by visible-light and infrared telescopes. Seeing in three dimensions made possible the discovery of a spiral structure surrounding R Sculptoris, providing new insights about how dying red giant stars implode and send off raw material that will later form into other stars. "Astronomy has been with us forever and we still have so much more to go," said Jose Maza, a University of Chile astronomy professor. "If we hadn't asked ourselves so many questions by looking at the stars we would still be ... hunting buffaloes. At the end, all of man's development comes from the act of leaving the stones aside and looking upward at the twinkling stars and asking, 'Why?'"