Academic journal article Science and Children

Charting the Skies of History

Academic journal article Science and Children

Charting the Skies of History

Article excerpt

Ice cores and ancient sediments can be gleaned for clues to weather and climate in the past. But astronomical phenomena such as solar flares or auroras at best leave only faint environmental traces. So how can we accurately track ancient astronomical events? The answer lies in historical documents.

Researchers have reconstructed a chronology of past astronomical events based on aurora sightings in Meigetsuki ("The Record of the Clear Moon," circa 1180-1241) by Fujiwara no Teika of Japan and in Song Shi ("History of Song," commissioned in 1343) from China.

"An early Japanese record of prolonged auroras, that is, auroras that persisted for two or more nights within one week, was documented February 21-23, 1204, in Meigetsuki," says lead researcher Ryuho Kataoka. "At the same time in Song Shi, a large sunspot was recorded on the 21." Such sunspots are an indication of intense magnetic activity on the Sun, including solar flares.

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The researchers looked further into Song Shi to see if there were additional indications of auroras between the years 900-1200 and found that there were 10 incidents of prolonged auroras during this time.

"When these dates were compared with radiocarbon data from tree rings, we noted decreased levels of carbon-14, indicating increased levels of solar activity at these same points," says Kyoto University historian Hisashi Hayakawa.

The team discerned that auroras were more prevalent in the maximal phase of solar cycles rather than the minimum and that no auroras were observed during the Sun's least active cycle between 1010-1050. …

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