Creator of stars

Powerful lasers leave the dome of one of the four Unit Telescopes of ESO’s Very Large Telescope (VLT) at Paranal Observatory in Chile. The beams reach a layer of the atmosphere about 90 kilometres above the ground, very rich with atoms of sodium. The lasers make the sodium shine, creating artificial stars in the sky. But why?

Earth’s atmosphere distorts light reaching us from cosmic objects, decreasing the sharpness of astronomical observations. This is the same reason why stars seen from Earth appear to “twinkle”. 

To correct observations for this effect, astronomers have developed a technology known as adaptive optics, where a flexible mirror is deformed hundreds of times per second to counteract atmospheric turbulence. However, to calculate the necessary corrections, adaptive optics need reference stars close to the observed object. Such stars are not always ideally placed, though, which made astronomers come up with the idea of using lasers to have artificial stars optimally located in the sky any time they are needed.

Fun fact: those sodium atoms are left over from meteoroids which terminated their journey across the Solar System by entering and burning up in the Earth’s atmosphere. So, in a way, when we excite those sodium atoms with lasers we are using space matter to help us observe space!