On This Day: September 23, the planet found with a pen

On the night of 23 September 1846, at the Berlin Observatory, Johann Gottfried Galle aimed a telescope at a patch of sky that Urbain Le Verrier had worked out on paper, and there it was: Neptune, within one degree of the predicted spot. It had been seen before, more than once, and written down as a star. The arithmetic didn't make the planet. It only said look here.

Francois Arago said Le Verrier had discovered a planet “with the point of his pen.”

Le Verrier never saw it himself. He said where to look, and someone else went out at night and looked.

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Have a date that matters? I write On This Day letters. [email protected]