This image shows comet Leonard streaming through the sky on the morning of 7 December 2021, taken by ESA’s Near-Earth Object Coordination Centre (NEOCC), part of the Agency’s Planetary Defence Office, using the Calar Alto Schmidt telescope in Spain.
By superimposing a ‘stack’ of 90 images each five seconds ‘long’, the comet is revealed whizzing past background stars which appear here as colourful streaks going from green to red to blue – colours chosen to signify the three different filters used to observe Leonard.
Centred around the comet’s bright nucleus, these artificial colours come together to create a brilliant white glow of the nucleus, while the green-bluish hue around it is true-to-life, the typical colour emitted by comets due to their chemical composition.