Suppose you want to glimpse the beginning of time, the very first moments of cosmic creation. You might start by building a perfect telescope, an instrument so powerful that it could see to the far end of the observable universe. You'd scout out a dry mountaintop, far from the star-fading glow of civilization. You'd level out a perch near its peak and place a state-of-the-art observatory atop it. You'd outfit it with a gigantic mirror—something much larger than could be launched into space—and equip it with a series of sophisticated detectors. You'd spend several years and several billion dollars, so that every last photon was within your reach. But what could you see with it? Say it was that one night in an astronomer's thousand, when the moon hides below the horizon, and the sky appears as a clear, dark dome overhead. What jewels would glitter out from that purplish-black showcase of celestial sights?
Quite a few, it turns out. In the foreground, you would see a smattering of planets, their orbits adrift against the fixed whirl of the constellations. Beyond them, local stars would loom large against a backdrop of fainter specks of white. In the sky's darker corners, galaxies would glow, some from hundreds of millions of light-years away. If you pointed your perfect telescope at exactly the right spot, it could reveal deeper cosmic recesses still. It could take you to the very first stars—the huge hydrogen and helium spheres, whose fiery surfaces illuminated the young universe.