Twilight Glow

The low twilight Sun highlights the clouds hanging over the Chilean Atacama landscape in this Picture of the Week, bathing the scene in deep, fiery red light. The image is dominated by the Purico Complex, a clump of volcanic mountains whose highest peak reaches a whopping 5703 metres in elevation! A single vehicle is visible on the remote road below, kicking up a stream of opaque dust in its wake, and towards the left of the image is a cluster of buildings...and a single antenna.

This is the ESO-operated Atacama Pathfinder Experiment (APEX), one of the highest telescopes in the world. APEX is designed to work at submillimetre wavelengths between infrared light and radio waves, which are key to revealing some of the coldest, dustiest, and most distant objects in the Universe. Over the years, it has explored a wide range of astronomical phenomena, probing the wild early lives of today’s most massive galaxies, studying matter torn apart by a supermassive black hole, and mapping the plane of the Milky Way. 

Because submillimetre radiation from space is heavily absorbed by water vapour in the Earth's atmosphere, it is best to observe it from high altitudes — hence APEX’s location. The experiment can be found at an altitude of 5100 metres, up on the Chajnantor plateau in Chile’s Atacama Desert. This desert is one of the driest places on Earth, and as such offers unsurpassed views of the cosmos. The site is also home to the Atacama Large Millimeter/submillimeter Array (ALMA), the world's largest ground-based facility for observations in the millimetre/submillimetre regime. ALMA’s 66 high-precision antennas are not visible in this image; they are scattered across the plateau behind the photographer.