Observing at One Wavelength

For most of human history, astronomy meant looking. Eyes, then lenses, then mirrors, then glass plates bolted to bigger mirrors. The instruments got magnificent. The band never moved. We surveyed the entire universe through a slot roughly three hundred nanometres wide, declared the catalogue essentially complete, and settled in to argue about the decimal places. The universe, meanwhile, was doing nearly all of its interesting work somewhere else. The sky was never quiet, we wereIn 1932 Karl Jansky was paid by Bell Labs to hunt down the static ruining transatlantic radiotelephone calls. He found a hiss that rose and fell with the sidereal day rather than the solar one, which is a polite way of saying that something in Sagittarius was screaming continuously and had been for the entire duration of recorded human civilisation. The astronomical establishment greeted this news with the enthusiasm of a homeowner informed that his house has a basement. Interesting. Perhaps later. What…