Solar sketches from 18th century solve sunspot mystery

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Washington, July 31 (ANI): Scientists have had a second look at sunspot drawings from the 1700s to solve a puzzling episode in the sun's history, which could lead to more accurate forecasts of dangerous solar outbursts.

The sun sometimes hurls clouds of plasma our way, which can fry satellites and knock out power grids on Earth.

The outbursts are most common during solar maxima, when the dark blemishes of sunspots appear in greatest abundance on the sun.

Although there is an average of 11 years between solar maxima, predicting the exact timing and height of each peak is difficult as there is little historical data to plug into models.

About two dozen solar cycles have occurred since reasonably complete records began.

Now, according to a report in New Scientist, an analysis of historic sunspot drawings suggests that this patchy record had omitted a solar cycle from the late 1700s.

Sunspot numbers for this period were compiled by Swiss astronomer Rudolf Wolf in the 19th century, who based his tallies on drawings of the sun made by Austrian amateur astronomer Johann Staudecher.

Wolf's numbers suggested there was a 15.5-year-long solar cycle between 1784 and 1799, the longest on record.

However, astronomers have long questioned the reliability of these numbers, since Staudecher's observations from this period are sparse.

To clear up the debate, a team led by Ilya Usoskin of the University of Oulu in Finland re-examined Staudecher's original drawings, currently held at the Astrophysical Institute in Potsdam, Germany.

They also added information from a handful of sunspot drawings made by astronomer James Archibald Hamilton and his assistant at Armagh Observatory, Ireland, between 1795 and 1797.

The team looked at both the number of sunspots and their location on the sun - important as sunspots tend to appear 20 degrees to 30 degrees from the sun's equator when a new cycle begins, but gradually show up closer to the equator as the cycle progresses, rarely straying more than a few degrees from it by the cycle's end.

"Wolf used (Staudecher's) drawings, but only to count the number of spots. He didn't use the location information," said Usoskin.

The team's analysis suggests a new, weak solar cycle began around 1793. The sunspots in Staudecher's drawings started appearing about 20 degrees from the equator that year, and one of Hamilton's 1795 drawings shows a sunspot at 15 degrees.

This suggests that in place of one unusually long solar cycle, there were actually two, lasting about nine and seven years, respectively, which may have had an effect on some of the forecast models. (ANI)

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