English: Can you see ESO’s New Technology Telescope (NTT) peaking out of its enclosure on the right of this Picture of the Week? When this telescope was inaugurated in 1989 it packed innovative technology that laid the foundations for all ground-based telescopes that would follow. The mirrors of professional telescopes are so large and heavy that they bend under their own weight; if left uncorrected, this would yield distorted images. The NTT, which is located at ESO’s La Silla Observatory in Chile, has a flexible main mirror that can change shape during observations. Using a so-called ‘reference star’, the NTT adjusts the mirror's shape to correct these deformations, thus ensuring optimal image quality. This technique, called active optics (not to be confused with adaptive optics) was developed by the late Raymond Wilson at ESO. Today, it is applied to all major modern telescopes, including ESO’s Very Large Telescope (VLT) at Cerro Paranal and the future Extremely Large Telescope (ELT), which is under construction on Cerro Armazones.But it wasn’t just a fancy mirror that made this telescope advanced: the enclosure around it was a technological breakthrough of its own. To help negate the detrimental effects of turbulent air within the dome, a system of flaps was installed to the housing of the NTT. These flaps ventilate the telescope, allowing air to flow smoothly over the mirror, helping the NTT capture crystal-clear images of the cosmos.