Notable for much more than his comet, the prodigy Halley started observing with Flamsteed even before the Royal Observatory was built. His catalogue of Southern stars made his name aged 22, though Flamsteed – never hurried, and later his professional enemy – criticised his hasty methods. Cassini, met in Paris, advised him on observing the transit of Mercury. Halley discussed the shape of an orbit with Wren and Hooke, but beaten by the maths, asked Newton for the answer. He knew Pepys and Arbuthnot well, met Leibniz en route to Vienna, and travelled to Danzig to resolve Hevelius and Hooke’s acrimonious dispute.