File:Into the vortex (potw2150a).jpg

English: This week’s picture may just hypnotise you! Resembling a vortex or an optical illusion, the starry circles draw you deeper into this breathtaking mountainous landscape of Chile’s Atacama Desert, home to ESO's La Silla Observatory.Each circular streak represents an individual star which maps out a star trail. Such trails are due to Earth’s rotation, which causes the stars to seemingly move across the sky, slowly tracing out perfect rings centred on the south celestial pole as they do so. A photograph like this therefore requires a long exposure to capture the passage of time. La Silla is located some 2400 metres above sea level, and offers perfect observing conditions for long-exposure shots like this; the site experiences over 300 clear nights a year! Here, ESO operates two of the most productive 4-metre class telescopes in the world: the ESO 3.6-metre telescope which is home to the world's foremost extrasolar planet hunter, the High Accuracy Radial velocity Planet Searcher (HARPS), and the 3.58-metre New Technology Telescope (NTT), the first in the world to have a computer-controlled main mirror (active optics).