The following is an article from issue 6 of All About Space, on sale now.
High in the Atacama Desert of northern Chile, construction is nearing completion on what will be the biggest telescope array the world has ever seen. Composed of 66 separate radio telescopes, the Atacama Large Millimeter Array (ALMA) is a mammoth project that will allow us to observe the universe with vision ten times sharper than the Hubble Space Telescope.
The exact location of this huge project is the Chajnantor plateau at 5,000 metres (16,400 feet) altitude. It is an international partnership between Europe, the US, Canada, East Asia and the Republic of Chile. With a price tag over a billion dollars it is the most expensive ground-based telescope under construction, but its capabilities once it is completed will be more than worth the cost.
Construction on ALMA began in 2004 and its first scientific observations with some of the antennas that have already been positioned began in late 2011. The operational capabilities of this array are unique. Each of the 66 antennas can be moved across the desert using giant transporter vehicles, allowing the array to be configured for the type of observations it will do. At its widest, the array will span 16 kilometres (10 miles), allowing astronomers to glean wide-angle images of the night sky. At its narrowest, just 150 metres (490 feet), much more focused views of a specific object can be taken.
All the antennas can be trained to point in the same direction for ultimate focus, known as interferometry, or they can each observe a different portion of the night sky to simultaneously study various cosmic features. 50 of the high-precision antennas are 12 metres (40 feet) in diameter, while 16 of them are 7 metres (23 feet).
ALMA has an impressive range of possible applications. It will be used to study the chemical and physical compositions of interstellar dust and gas and observe some of the earliest and most distant galaxies in the universe, amongst much more. This is thanks to its use of submillimetre astronomy, which allows it to observe areas that would otherwise appear dark in visible light.
ALMA is due for completion in 2013. It will hold the accolade of largest telescope array until the completion of the Square Kilometre Array in 2024.