Location of the observatories used in an EHT pilot experiment

In this world map, the yellow dots mark the location of the antennas and arrays that participated in a pilot experiment conducted by the Event Horizon Telescope (EHT) Collaboration. The experiment was the first time that the very long baseline interferometry technique, which connects telescopes hundreds or thousands of kilometers apart, was successfully used to observe light at a wavelength of 0.87 mm. By observing light at this lower wavelength, the EHT researchers were able to get higher resolution observations than they had before, without forming a bigger telescope. The detections made have the highest resolution ever obtained from the surface of Earth. 

The facilities that participated were: the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Pathfinder EXperiment (APEX), in Chile, the IRAM 30-meter (30-M) telescope in Spain and the NOrthern Extended Millimeter Array (NOEMA) in France, as well as the Greenland Telescope (GLT) and the Submillimeter Array (SMA) in Hawaiʻi. ESO is a partner in ALMA and co-hosts and co-operates APEX.