At 5000 meters above sea level in a Chilean desert sits the Atacama Large Millimeter Array (ALMA). This array consists of 66 radio telescope dishes and was officially opened in March 2013. This marvel of technology has already peered through cosmic dust clouds in the milky way to observe planet formation and distant galaxies. However working in these extreme conditions where chapped skin, altitude sickness and low temperatures are an everyday occurrence is taking its toll on the operating crew. ALMA has currently been taken offline whilst the various personnel living and working up on the Chajnantor plateau negotiate with their associated universities for a 15% pay rise with extra benefits.
The reason behind the array being located in such a harsh environment is to do with the nature of making radio observations. In the long wavelength section of the electromagnetic spectrum the atmosphere (especially water) absorbs radiation from astronomical sources. Therefore in order to observe in this region a high and dry condition is needed to give the best possible observing conditions.
You may also ask yourself why have they had to use an array? Why couldn’t they use one radio dish as a telescope? The answer comes from a bit of simple physics regarding the angular resolution of a telescope. The relationship between the angular resolution (θ), wavelength of observed radiation (λ) and the telescopes diameter (D) is;
This equation means that the longer the wavelength being observed the wider the diameter of the telescope itself needs to be in order to have a small enough angular resolution so that the distant objects can be viewed. In visible light (λ=550nm) to obtain a reasonable resolution only requires up to meters in diameter, whereas radio astronomy (λ>mm) would require a single antennae diameter of many kilometers. This is a massive problem, as this means the angular resolution is going to be nowhere near good enough for distant galaxy observations.
Hence the array approach is used which interlinks the radio dishes and allows the above relationship to be rewritten;
but where B is now the base line of the array. This base line refers to the distance between the two furthest antennae in the array. This now can allow a distance of kilometers to exist and hence vastly improve the resolution of observation.
The hope from everyone is that ALMA can resolve the monetary issues soon so that this wonderful radio telescope array can reach it’s full potential.