Capturing the cosmos with laser-sharp precision

Does this look like science fiction? Well, it is science, but definitely not fiction. In this Picture of the Week, the lasers of ESO’s Very Large Telescope (VLT) are creating artificial stars in the Chilean sky. It’s one of the clever ways in which engineers outwit the biggest enemy of ground-based telescopes: the Earth’s atmosphere.

When stars seem to be twinkling, this is the effect of turbulence in our atmosphere. It distorts the signals from space, leading to blurry images. That is why ESO’s telescopes are located high and dry in the desert: a thinner atmosphere means less disturbance. Modern telescopes use adaptive optics to counteract this disturbance and improve their resolution.

This is where the lasers come in. They create artificial stars 90 km up in the sky by making sodium atoms in the upper atmosphere glow. During observations, these guide stars are used as reference points, and a computer-controlled mirror deforms itself up to 1000 times per second to correct the atmospheric distortion. A clever trick, isn’t it? ESO’s Extremely Large Telescope, which is currently under construction, will also be equipped with this nifty system, in addition to housing the biggest telescope mirror ever built. So get ready for even sharper images of the Universe!