In astronomy, bigger is almost always better. The size of a telescope's aperture (or primary optical element) not only determines how many pesky little photons it can capture, but also the ultimate resolution of the image that can be formed. The challenge is to fabricate optics on large scales, find somewhere really good to put them, and to build the massive structure to house them and the sensitive instruments to analyze the photons that come out of the pipeline.
Now one of the world's next generation of huge telescopes has been given the green light to push ahead with construction and operation. At an astonishing 39.3-meters in diameter, the European Extremely Large Telescope, or E-ELT (one can only hope a more poetic name is eventually chosen) will hold the crown for sheer girth among optical and infrared sensitive telescopes. With an authorized spending of about a billion euros (about $1.24B) the project can move ahead, with an anticipated 'first light' sometime in 2024.
To put E-ELT into perspective, here's a comparison chart.
Although E-ELT is not alone in the race for so-called '30-meter class' telescopes (with the Thirty Meter Telescope and Giant Magellan observatories also on track, and also extraordinarily powerful), it's definitely the Hulk of the bunch.
Observatories on this scale will have profound impact on how we study the universe around us, from cosmology to planets.
A telescope like E-ELT will peer at the faintest, most distant objects in the young cosmos, and it'll be capable of sensing the atmospheric signatures of life in a few nearby terrestrial-type exoplanets (including the presence of oxygen). These tasks require an enormous 'light bucket' to catch enough photons, but perhaps one of the most vivid examples of the gain of a big telescope comes from considering the resolving power.
Equipped with adaptive optics E-ELT should, for example, be able to routinely study Jupiter down to scales of about 20 kilometers - by comparison the Great Red Spot is at present about 20,000 kilometers across. Mars can be imaged to roughly 5 kilometer resolution (depending of course on the relative separation of Earth). In other words, on a nightly basis we will be able to monitor the worlds in our solar system with a fidelity comparable to fly-by missions of yore.
Preparations have already begun. In June 2014 explosives were used to help level the mountaintop where E-ELT will sit - Cerro Armazones in northern Chile, a dry peak at about 3,000 meters altitude where the night skies are cloudless 89% of the time.
What rises there over the next ten years will help take our understanding of the universe to a whole new level.