Satellite reflections over CTA Site

Hundreds of astronomical objects are visible in this ESO Picture of the Week, including star clusters, nebulae, dust clouds, and other galaxies — most notably the Large and Small Magellanic Clouds, visible to the upper right. However, something much closer to home is vying for our attention. To the far right of the image, a silver arc streaks across the sky. This arc is actually composed of two closely-spaced lines, caused by sunlight bouncing off the antennae of two Iridium communication satellites currently orbiting the Earth.

It may be empty now, but this dry, barren section of the Chilean Atacama Desert will soon be bustling with activity. The site has been selected to host the southern part of the Cherenkov Telescope Array (CTA), a remarkable array of 99 antennas that will gaze up at this incredible sky in search of high-energy gamma rays. Gamma rays are a type of electromagnetic radiation that is emitted by the hottest and most powerful objects in the Universe — supermassive black holes, supernovae, and possibly remnants of the Big Bang itself.

However, the Earth’s atmosphere prevents gamma rays from reaching its surface, so rather than hunting for these rays directly the CTA will observe something known as Cherenkov radiation — ghostly blue flashes of light produced when gamma rays interact with particles in our atmosphere. Pinpointing the source of this radiation allows each gamma ray to be traced back to its cosmic source. Just like its neighbour, ESO’s Very Large Telescope, the CTA requires a dry, isolated location to do its work successfully — and for this the Atacama is perfect.