This spherical panorama was photographed from the center of the Japanese 7-m antenna array located at the 5000 meter altitude ALMA* Array Operations Site. Japan was responsible for developing the Atacama Compact Array (also known as the Morita Array) which consists of a total of 16 antennas: four 12-m antennas and twelve 7-m antennas. As the name implies, the 7-m antennas are crowded together so compactly that it seems as though they might touch.

The Reason for Crowding the Antennas Together

For interferometer type telescopes like ALMA, the angular resolution improves as the separation between the antennas increases. On the other hand, the drawback is that when the separation is wide, it becomes difficult to detect the radio waves from faint, extended astronomical objects. To overcome this drawback it is necessary to crowd the antennas close together. But 12 meter diameter antennas cannot be brought closer together than about 15 meters at best. So by crowding smaller, 7-m antennas close together, the Morita Array developed by Japan can detect the radio waves from extended celestial objects which the 12-m antenna array developed by Europe and the United States of American cannot capture. This enables ALMA to take accurate radio photographs of actual celestial objects.

*Atacama Large Millimeter/submillimeter Array

Text by: Masaaki Hiramatsu (NAOJ Chile Observatory / Public Relations Center)
Translation by: Ramsey Lundock (NAOJ)