The ESO 3.6-metre telescope at La Silla, during observations, with the telescope's dome lit by the Moon. Across the sky is the plane of the Milky Way, our own galaxy, a disk-shaped structure seen edge-on. Above the telescope dome, and partially hidden behind dark interstellar dust clouds, is the prominent yellowish central bulge of the Milky Way. The plane of the galaxy is populated by hundreds of billions of stars, as well as interstellar gas and dust. The dust absorbs the visible light and re-emits it at longer wavelengths. Where it forms dense dust lanes, it appears dark and opaque to our eyes. The ancient Andean civilisations saw in these dark lanes their animal-shaped constellations. By following the dark lane which seems to grow from the centre of the Galaxy toward the top, we find the reddish nebula around Antares (Alpha Scorpii). The Galactic Centre itself lies in the constellation of Sagittarius and reaches its maximum visibility during the southern winter season. The ESO 3.6-metre telescope, inaugurated in 1976, currently operates with the HARPS spectrograph, the most precise exoplanet “hunter” in the world. Located 600 km north of Santiago, at 2400 m altitude in the outskirts of the Chilean Atacama Desert, La Silla was the first ESO site in Chile and the largest observatory of its time.
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