Rebecca Elson was an astronomer. Her work took her to the boundary of the visible and measurable. Facts are only as interesting as the possibilities they open up to the imagination, she wrote. Her research involved dark matter - hidden mass which can be inferred only from its influence on observable objects: As if, from fireflies, one could infer the field. Her poems, too, make inferences and speculate, setting out always from meticulous observation and not deterred by a knowledge of how little we can know of the universe.