Concentric Circles

In this eye-catching Picture of the Week, bright star trails fill the sky above ESO’s La Silla Observatory in Chile. Such trails are formed by the Earth spinning on its axis — our planet’s rotation causes the stars to seemingly move through the sky, slowly tracing out perfect concentric arcs and circles as they do so. A photograph like this therefore requires a long exposure to capture the passage of time.

At the centre of this image is the decommissioned Swedish-ESO Submillimetre Telescope , and the ESO 3.6-metre telescope sits atop the mountain to the left, aglow with activity. This telescope hosts HARPS (the High Accuracy Radial velocity Planet Searcher), which searches for exoplanets by measuring the tiny “wobbling” motions of their host stars as the planets sweep around in their orbits.