‘A New Window’

Abstract

The night sky is a window onto the Universe. During the day the sunlight is scattered by the air molecules and obscures our view. For astronomers, it’s like trying to watch a film at the cinema with the lights on. But when the Sun sets, the sky darkens and we see Earth’s celestial surroundings. Since prehistory, humans regarded the night sky as a hemispherical surface to which the stars were attached, but now we know better: with insight the dark dome of the sky disappears and we are free to peer deeply into space. The difference in the apparent brightnesses of the stars is a combination of intrinsic luminosity and distance, but generally speaking the fainter stars are further away. The further we look the more numerous the stars. At some point they cease to be individuals and merge to form the ghostly band of the Milky Way just as sand grains merge to form the smooth texture of a beach. Diffuse patches just visible to the naked eye are galaxies themselves far beyond our own. As technology advances, so does our perception, but there is no obvious end to what we will discover. The sky has neither surface nor limit: when we look into the night sky we are humbly yet irresistibly peering into the cosmos. Yet there is more to the Universe than meets the eye: there exists a universe invisible to our natural senses, and like so many major scientific developments, this new universe was unveiled completely by accident. Ironically, it was initially explored not by astronomers who had devoted their lives to watching the skies, but by radio engineers intent on winning a war.