At 16,000 feet and in the rain shadow of the Andes Mountains, northern Chile’s virtually cloudless, extremely arid Atacama Desert1 provides an ideal location for large telescopes. Free from light pollution and radio interference, this desolate area is home for a new radio astronomy facility called the Atacama Large Millimeter/submillimeter Array, or ALMA.2
ALMA operates at a range of wavelengths of between 0.3 to 9.6 millimeters; therefore any moisture in the atmosphere will affect measurements. By putting the facility where the atmosphere is thin and very dry, astronomers will achieve unprecedented sensitivity and resolution, almost as good as being in space but far cheaper.
When completed in 2012, ALMA will be a single research instrument composed of up to 80 high-precision antennas, each 12 meters (m) in diameter (see figure 1). By spreading the antennas out over a maximum distance of 18 kilometers (km), the instrument will be able to synthesize a portion of the sky with resolutions as fine as 0.005 seconds of arc at its shortest wavelengths, a factor of ten better than the Hubble Space Telescope.
To visualize how an array works, picture a single reflecting telescope having a primary mirror with a diameter equal to the maximum size of the array, in this case 18 km. Such an instrument would have fantastic light-gathering power and resolution because of its enormous size. Imagine masking out most of the mirror’s surface except in 12 m circles corresponding to the placement of the array antennas. The effect reduces the telescope’s light-gathering power but its resolution remains the same. However, the image made with such a telescope creates “artifacts” caused by the masked areas of the mirror. But, if the antennas are properly spaced, these artifacts can be minimized over a sufficiently large portion of the image, resulting in a picture hardly different than one made with an 18 km telescope!
Excitement builds as astronomers anticipate a wealth of information. Because of its size and location, ALMA will be capable of producing detailed images of the formation of galaxies, stars, and planets. The instrument will image stars and planets forming in gas clouds near the Sun, and it will observe galaxies in their formative stages at the edge of the universe.
Despite its harsh environment, ALMA will draw researchers hoping to peer through this window on celestial origins. RTB scholars stand to benefit from the new discoveries such an instrument will permit as it tests RTB’s creation model predictions.