ALMA – the Atacama Large Millimeter Array
Otto
Otto is one of two transporters used to move the antenna dishes around (the other is called Lore). It is 10m wide, 20m long and has 28 wheels.
As well as transporting the 100-ton antennae between the Control centre and the plateau, these vehicles are used to reposition the dishes to an accuracy of a few millimeters.
Antenna Maintenance
ALMA is designed to ‘see’ in the millimeter and sub-millimeter wavebands – roughly where microwave ovens emit radiation.
Because water vapour in the atmosphere absorbs these wavelengths, ALMA is situated on the Chajnantor plateau, 5000m high in the Atacama desert, one of the driest places on the planet – some parts of the desert have not seen rain in 100 years.
ALMA comprises 66 dish antennae that together form a powerful interferometer, whose resolution can be varied by moving the dishes around the site. However as each dish weighs over 10 tons and has to be positioned with millimeter accuracy, special vehicles are needed to transport them (see below).
Because of the altitude and extreme sensitivity to radio noise, visitors are not allowed on the actual ALMA site, but the control centre (at a mere 2,900m) welcomes tour groups and this is where the antennae are brought for periodic maintenance.
The photo shows one antenna awaiting attention in the maintenance facility.
Lascar Volcano
Our group was treated to some spectacular views of volcanoes as we left the Atacama for the journey to Antofagasta.
There are some 500 active volcanoes in Chile and Lascar is among the tallest at 5592m (18,346ft). It has two separate cones with several summit craters. It is also one of the most active is this region having last erupted in 2015.
This image displays orographic clouds around two or three of the peaks. These are not volcanic in origin but are formed when air forced upward as it encounters mountains then cools due to expansion to the point where it becomes saturated with water vapour and cloud is formed. The clouds often disappear as the air falls back down the far side of the mountain and warms up again.
