Medieval Korean Records Corroborate English Observation of Sunspots

On December 8, 1128, John of Worcester created a colorful drawing of the Sun, the first of its kind in the world. His sketch revealed two sunspots¿dark patches on the Sun's surface that we now know are giant magnetic storms sometimes visible with the naked eye. Although accounts from China had described sunspots more than 1,000 years earlier, no one up until then had bothered to depict them.

But the Englishman wasn't the only one watching the skies at the time. Researchers from the University of Warwick and the University of Durham in England recently found a passage in the Koryo-sa¿the official Korean chronicle of the time¿that speaks of an unusual phenomenon five days after John of Worcester's observation, on December 13, 1128. Indeed, the text described a red light in the night sky above Songdo, the modern city of Kaesong.

The researchers say that although John of Worcester looked at the Sun and the Korean observer looked at the night sky, the phenomena they saw were directly linked. Sunspots occur near solar flares, which shoot particles out into space. When these particles reach Earth, they hit the thin gases of the upper atmosphere, causing auroras, which is what the Korean historian saw. And the time lapse between the appearance of large sunspots and aurora borealis at relatively low latitudes is about five days.

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