A Green Nomad above Giants

It may not be as famous as Halley’s Comet, but Comet 252P/LINEAR can still put on a show! In late March 2016, the comet made one of the closest approaches to Earth of all comets in history — just over 5.3 million kilometres distant, compared to Halley’s closest approach of 87 million kilometres. The light of Comet 252P/LINEAR is not elongated in a classic tail, but instead appears as a soft round glow, tinged green due to molecules of diatomic carbon fluorescing in the sunlight. This image from April 2016 captures the distinctly green comet: you can spot it just above the Milky Way, between the galaxy’s starry arch and the Very Large Telescope (VLT) Unit Telescope at the centre of the frame.

ESO’s VLT is located at the Paranal Observatory in Chile, an ideal location for comet-spotting. Paranal is one of the most spectacular observatories in the world, situated in the seemingly infinite Atacama Desert under the dark skies of the southern hemisphere. Comets are not the only treasure visible in these skies: the Milky Way puts on its nightly spectacle, its rich interstellar clouds bejewelled with stars, the diverse colours of natural airglow shine near the horizon, and high above sit two planets. In this sweeping panorama, they form a slightly distorted triangle that includes the red supergiant star Antares, with the intense shine of Mars to the left and the whitish glow of the gas giant Saturn beneath.