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Summer 2000

Century-old sunspot chart is restored

by Carol Rasmussen

Thomas Bogdan holding the Maunder diagram. (Photo by Carlye Calvin.)

For more than 50 years, NCAR's High Altitude Observatory has housed a chart drawn in 1904 that illustrates a breakthrough in solar physics. At the June meeting of the American Astronomical Society, HAO scientist Thomas Bogdan explained how the chart ended up in Climax, Colorado, at the height of World War II.

The chart is called the Maunder butterfly diagram because of its resemblance (with the help of a little imagination) to three butterflies traveling west. Drawn by E. Walter Maunder and Annie S.D. Maunder, it demonstrated for the first time the movement of sunspot emergence from the poles toward the equator over the sun's 11-year cycle. According to Bogdan, even today, almost a century later, solar theorists have not developed a full explanation of why spots move toward the equator.

As Annie Maunder described it, "We made this diagram in a week of evenings, one dictating and the other ruling these little lines. We had to do it in a hurry because we wanted to get it before the [Royal Astronomical] Society at the same meeting as the other sunspot observers, whose views we knew to be heretical. As it turned out . . . the diagram wiped [the other observers'] papers clean off the slate."

The Maunders certainly knew their sunspots. Walter was an assistant in the solar department of the Greenwich Royal Observatory in England; he had been photographing the sun since the department was founded in 1873. Annie worked with Walter at the observatory as a "lady computer" from 1891 until they married in 1895. She was an unusually well-educated woman for her time; she had passed the Cambridge University degree examinations with honors in mathematics, though she was not allowed to receive a degree. Although Annie was required to resign when she married her boss, the two continued to work together on their own. Annie accompanied Walter on eclipse expeditions and developed a camera for photographing the corona. Walter died in 1928.

In 1943, while London was being bombed nightly by the Nazis, Annie got a letter from a friend named Stephen Ionides. Born in London, Ionides had led an adventurous life as an engineer and miner in England, Australia, Mexico, and the American West before settling in Denver. Ionides' hobby was science history, and he asked Annie for a drawing. To save the butterfly chart from destruction in the Blitz, she gave it to Ionides.

Later that year, Ionides attended a talk by a young astronomer from Climax, Colorado—Walter Orr Roberts, the founder of HAO. Ionides invited Roberts to his home, where Roberts saw the butterfly. "Walt was totally overwhelmed, because he understood the significance of it," says Bogdan. A few days later, Ionides mailed the chart to Roberts at Climax, saying it should be on display. Annie Maunder later wrote to Roberts, saying how glad she was that the chart had a safe home. She died in 1947. When HAO joined NCAR in 1960, the chart came along.

Bogdan, an NCAR scientist since 1983, is researching the history of HAO in hopes of writing a book. "For 17 years I walked by this picture of butterflies in kind of a cheesy frame," says Bogdan. "I only found out what it was while working on the HAO history." He made an archival-quality print and had the original reframed using acid-free paper and ultraviolet-resistant glass. "Since it survived the 20th century," he says, "I'm getting it ready for the 21st."

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Edited by Carol Rasmussen, carolr@ucar.edu
Prepared for the Web by Jacque Marshall
Last revised: Fri Sep 1 16:44:56 MDT 2000