BBC Earth (Asia) - - Q&a -

On the night of 23 Septem­ber 1846, the Ger­man as­tronomer Jo­hann Galle no­ticed an ob­ject in the con­stel­la­tion Aquarius which didn’t ap­pear on the lat­est star maps. Its disc-like ap­pear­ance sug­gested it was a new planet – a con­clu­sion con­firmed the fol­low­ing night by its move­ment rel­a­tive to the dis­tant stars.

Galle had dis­cov­ered Nep­tune, but it was no ac­ci­dent. He had been asked to ex­am­ine that patch of the night sky by Ur­bain Le Ver­rier, a bril­liant French the­o­reti­cian who had been ex­am­in­ing strange ef­fects in the or­bit of Uranus, and con­cluded it was be­ing af­fected by an un­seen planet. But just as Galle and Le Ver­rier were be­ing hailed for their dis­cov­ery, Bri­tish astronomers claimed a young Cam­bridge math­e­ma­ti­cian, John Couch Adams, had made sim­i­lar cal­cu­la­tions, and that a Bri­tish as­tronomer had sub­se­quently seen Nep­tune three times – but failed to recog­nise it. This at­tempt to grab some of the glory sparked an in­ter­na­tional row – which in­ten­si­fied when Amer­i­can astronomers ar­gued that the pre­dic­tions were faulty, and the dis­cov­ery merely a “happy ac­ci­dent”. Re­cent re­search has led his­to­ri­ans to dis­miss the Bri­tish claim. But it’s now known Galle wasn’t the first to see Nep­tune: stud­ies of Galileo’s note­books show he un­wit­tingly saw it as early as 1612. RM

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