HAL­LEY’S COMET

BBC Earth (Asia) - - Q & A -

The most fa­mous of all comets was cer­tainly seen by the English as­tronomer and math­e­ma­ti­cian Ed­mond Hal­ley when it flew round the Sun in 1682, but he did not dis­cover it. The credit for that goes back at least another 2,000 years to 240 BC, when un­known Chi­nese astronomers noted what they called a ‘broom star’ ap­pear­ing in the east­ern sky in May of that year.

Hal­ley’s claim to the name stems from his cru­cial dis­cov­ery about the na­ture of the epony­mous ob­ject. While study­ing a list of comet ob­ser­va­tions over the cen­turies, he no­ticed that the years 1531, 1607 and 1682 all fea­tured the ap­pear­ance of one of these sup­pos­edly capri­cious por­tents of doom. Was it just a co­in­ci­dence that they were all about 76 years apart? Us­ing New­ton’s then newly pub­lished law of grav­ity, he showed that they were all the same ob­ject, swing­ing round the Sun on a vast or­bit. Hal­ley pre­dicted it would re­turn in 1758, which it duly did. While he didn’t live to see it, his cal­cu­la­tions played a key role in show­ing that sup­pos­edly fickle nat­u­ral phe­nom­ena can be un­der­stood through the power of science. RM

CHI­NESE ASTRONOMERS

ED­MOND HAL­LEY

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