What’s that coming over the hill? It’s ALMA!

It might look like there’s not a lot going on in this Picture of the Week, but looks can be deceiving. Far off in the distance, huddled together like penguins in an Antarctic storm, sit the 66 high-precision antennas of the Atacama Large Millimeter/submillimeter Array (ALMA). Operated by ESO together with international partners, ALMA is designed to study the light emitted by the coldest objects in the Universe, such as vast cold clouds in interstellar space.

Stretching out either side of the antennas is the empty landscape of the Chajnantor plateau. Sitting at 5,000 m above sea level in the Chilean Andes, this remote location is one of the driest places on Earth. It’s this dryness that makes it the perfect place for observing the signals from the cold Universe which would otherwise be heavily absorbed by water vapour in our atmosphere. 

ALMA is what’s known as an interferometer, meaning that its individual antennas work together, acting to form a more powerful telescope that can discern details smaller than what can be seen with the individual antennas. Depending on what observations are being carried out, the antennas are arranged in different configurations. The further away they are, the finer the details they can see; more compact configurations, on the other side, offer better sensitivity and are ideal when observing diffuse extended objects. Here the antennas are in one of the most compact configurations, but the distance between them can be as great as 16 kilometres!