ahoxus pleroma

This is one of the most spectacular sunsets I ever saw while working at ESO's Paranal Observatory in Chile.

The Atacama Desert is extremely dry, but clouds do show up sometimes. That day there were several dark clouds releasing very light rain that vaporised before reaching the ground. These wispy veils (called "virga") were lit by the golden sunset light, creating a lovely contrast with the blue sky above.

A stormy sunset over ESO's Paranal Observatory. There are three identical white telescope domes, one to the lower-right in the foreground and two to the background at the center left. The sky is blue, with several dark clouds. There are wispy veils of rain that don't quite touch the ground. These veils as well as the telescopes are bathed in the golden sunset light coming from the right (the Sun itself isn't visible in this image).

The telescopes you see here are 3 out of our 4 Auxiliary Telescopes. Each one has a 1.8 m mirror. These telescopes work together using a technique called interferometry: by combining their light we can achieve the resolution of a "virtual" telescope as large as the separation between the individual telescopes.

One cool thing about these Auxiliary Telescopes is that we can move them along rails! By changing the separation and orientation of these telescopes we can probe different levels of detail in the astronomical objects we study.


We have four other larger telescopes called Unit Telescopes, each one with an 8.2 m mirror. These normally work as standalone telescopes, each one pointing at a different target. But we can also link them with interferometry.

If you want to learn more about this technique, check out this explainer that we prepared!


@astro_jcm next time, make a video please! 🥰