[2][3] Koyama worked as a staff member of the National Museum of Nature and Science, Tokyo for more than 40 years and completed more than 10,000 solar sketches during her lifetime.

Before she began her career as a staff observer, Koyama would read books about astronomy and go star watching with astronomical charts.

During World War II, she would use city-wide air-raid blackouts as opportunities to set up a futon in her yard and make celestial observations.

In 1944, she submitted her first sunspot sketch to Issei Yamamoto, professor of astronomy at Kyoto University, who was serving as Oriental Astronomical Association Solar section president at the time.

The project also relied on sketches drawn by Galileo Galilei, Pierre Gassendi, Johann Caspar Staudacher, Heinrich Schwabe, and Rudolf Wolf.