7-metre ACA antennas

Three 7-metre antennas are pictured alongside a 12-metre antenna in this shot from atop the Chajnantor Plateau in northern Chile.

The Atacama Large Millimeter/submillimeter Array (ALMA) is a giant radio telescope composed of an array of fifty 12-metre antennas, as well as a smaller array known as the Atacama Compact Array (ACA) — featuring four 12-metre antennas and twelve 7-metre dishes.

The ACA is specifically designed to help ALMA make better observations. Its smaller 7-metre antennas can be placed closer together, making them better able to measure the broader cosmic structures that the main array misses.