Astronomy is the only branch of science where the questions are literally cosmic. Its practitioners are trying to answer the most profound questions imaginable, the same questions that philosophers have been wrestling with for thousands of years. How big is the universe? How old is it? What is it made of? Are we alone, or do other intelligent beings live on planets orbiting distant stars? How did the cosmos begin? And how will it end? As recently as a decade ago, none of these questions had been answered in any definitive way. Now, thanks to powerful new space-based observatories and ingenious new techniques for gazing up from the ground, astronomers have cracked some of them. We now know that the universe is 13.7 billion years old, that more than 100 planets circle Sun-like stars right in our celestial neighbour-hood, and that the cosmos is likely to expand forever, until all the stars have burned out and matter itself breaks down. We know that gamma ray bursts—explosions so massive they defied understanding for decades—are exploding stars more powerful than anyone had imagined. Yet plenty of mysteries remain. Astronomers know that the visible stars and galaxies add up to only a fifth or so of the matter in the universe. The rest is some sort of mysterious dark matter, detectable only through its gravitational influence on the visible stuff. The search for dark matter is still a major focus of modern astronomy. Closer to home, there's a major push to find not just planets, but Earthlike planets orbiting nearby stars. The massive, gaseous, Jupiter-like planets found so far are impressive enough, but as far as we know, you need something smaller and more solid to support life—the ultimate goal of planet-searchers. Indeed, while astronomers had long since given up looking for life in our own solar system, biologists have given them new hope. Life, it turns out, can live in far harsher conditions than anyone thought (hot springs, Antarctic ice, inside solid rock), which means it could exist under the surface of Mars or in oceans under the icy coating of Jupiter's moon Europa.
Strong lensing of gamma ray bursts as a probe of compact dark matter