Atacama Compact Array (ACA)

The Atacama Compact Array (ACA), also called the Morita Array, is a cluster of 16 smaller dish antennas — twelve 7-metre and four 12-metre reflectors — operating as a sub-array of the ALMA observatory on the Chajnantor Plateau in northern Chile at roughly 5,000 metres above sea level. The extreme aridity of the Atacama Desert makes the atmosphere here uniquely transparent to millimetre and submillimetre wavelengths, allowing astronomers to study star-forming regions, distant galaxies, and the cold molecular universe with unmatched precision. The ACA specifically captures large-scale diffuse emission that the longer-baseline ALMA antennas would filter out, making it an indispensable complement to the full array. Guided public visits to the ALMA site are offered on select weekends, giving rare ground-level access to the facility beneath one of Earth's darkest skies.