Galileo’s female Japanese peer

A female Japanese amateur astronomer has been posthumously recognised as one of the most important contributors to her field, being included alongside Galileo as a crucial authority on sunspots.

Hisako Koyama was born in Tokyo in 1916 and against extraordinary odds established herself as an expert on the solar phenomena. 

Sunspots were first noted in 1610. They appear as dark areas, the results of intense local magnetic activity that temporarily lower the Sun’s surface temperature. Sunspot frequency varies across the 11 years of the solar cycle.

A keen amateur, Koyoma made her first sketch of a sunspot in 1944, using a telescope that was a present from her father. She sent the result to the Japanese Oriental Astronomical Association. 

The work drew the attention of the association’s president, Issei Yamamoto, who then encouraged and mentored the young woman. Two years later she scored a job at what is now the National Museum of Nature and Science in Tokyo.

She was to remain there – compiling a record of more than 8000 sunspot events using the museum’s own telescope – until her retirement at the age of 65 in 1981.

She died in 1997. Today her meticulous records are recognised by astronomers as an essential part of a corpus of observations that comprise a 400-year record of sunspot activity. The other contributors to this universal resource are Galileo Galilei, Pierre Gassendi, Johann Caspar Staudacher, Heinrich Schwabe and Rudolf Wolf. 

Koyama’s work is the focus of a new study produced by a team led by Delores Knipp, a space weather scientist at the University of Colorado Boulder in the US, and published in the journal Space Weather.

In it, Knipp and her team describe her as “a most unusual woman of her time” who “bridged the amateur and professional world.” 

The authors note that “the path to science for a girl of any nationality born in the early twentieth century was formidable-to-nonexistent”, yet Koyoma succeeded in building a career for herself. Today, they add, she remains little known outside of professional circles despite her “her international contribution to understanding the symmetries and asymmetries of the solar cycle.”

Off the page, Knipp’s language becomes less formal, but no less respectful.

“Women scientists have been contributing in the sciences for a very long time, whether or not the documentation exists to that fact,” she says.

“This is my first attempt to make sure her record is revealed to a broader community, especially to young women considering science careers.”