A laser show on Paranal

It’s hard not to get sucked into this Picture of the Week, taken using a long exposure at ESO’s Paranal Observatory in the Chilean Atacama Desert. Above the mountaintop observatory, a spectacular dance is playing out: imaged over several hours, stars appear to make their way in long arcs, called star trails, across the night sky. 

Paranal is home to one of the world’s most advanced optical telescopes: ESO’s Very Large Telescope, or VLT. This flagship facility actually consists of four Unit Telescopes and four smaller movable Auxiliary Telescopes, like the one in the foreground on the right.

But what are those mysterious beams of orange light erupting from one of the Unit Telescopes? Well, they’re for making stars, kind of. The Four Laser Guide Star Facility propagates laser beams[1] into the sky, making sodium atoms in the upper atmosphere glow like artificial stars. Each laser delivers 22 watts of power — about 4000 times the maximum allowed for a laser pointer — in a beam that’s about 30 centimetres in diameter. This remarkable display doesn’t just look pretty: the twinkling of these artificial stars is measured in real time and used by the adaptive optics system to correct for the blurring caused by the Earth’s atmosphere so that the telescope can create sharp images.

Note 

[1] The beams in this image are pointing in opposite directions because this is a long exposure taken over several hours, during which the telescope moved to observe different targets in the sky.