"Half of all light in the universe is in millimeter-wavelength light between the far infrared and radio waves. ALMA can detect this light, which is emitted by cool objects and distant objects. It's possible thanks to the telescope's location at 16,400 feet in the driest desert on Earth, and because of the incredible precision of its 66 antennas.
All telescopes are limited in their angular resolution by the ratio of their aperture to the wavelength they observe, explained Michael Thornburn, head of the ALMA department of engineering. ALMA is an aperture synthesis telescope.
"We cannot make a single aperture 15 kilometers across, so we do it in pieces," he said. "The signals from individual dishes are combined to build up the image from a single large aperture."
Radio signals from distant cosmic sources arrive at each dish at ever-so-slightly different times, and these are combined with the signals from every other antenna. This technique, interferometry, allows ALMA to operate like a single huge dish with an adaptable radius.
In a carefully choreographed ballet, each dish moves in unison with the others to change the telescope's observing area. Along with moving in place, giant transporter trucks, specially designed for the dishes, can pick them up and cart them across the Chajnantor Plateau to one of 192 concrete pads. At their greatest distance apart--16 kilometers--ALMA's angular resolution will be equivalent to the Hubble Space Telescope, Peck said."