The ALMA cacti

Cacti enjoy a nice breezy day high on the Chajnantor plateau in the Chilean Andes. At this site, the European Southern Observatory (ESO), together with its international partners, is operating the Atacama Large Millimeter/submillimeter Array (ALMA) — a state-of-the-art telescope to study light from some of the coldest objects in the Universe. This light has wavelengths of around a millimetre, between infrared light and radio waves, and is therefore known as millimetre and submillimetre radiation. ALMA comprises 66 high-precision antennas spread over distances of up to 16 kilometres. This global collaboration is the largest ground-based astronomical project in existence.